fix: Fix EXTERNAL function call syntax across all NPC files

Fixed all player_name references to use function call syntax player_name().
Also removed invalid === END knot definitions from hub files.

Changes:
- Fixed player_name -> player_name() in all ongoing_conversations.ink files
- Removed === END knot definitions (END is a built-in directive)
- chen_hub.ink now compiles successfully with only warnings
- netherton_hub.ink and haxolottle_hub.ink still have some structural issues to resolve

Status:
✓ chen_hub.ink - compiles successfully
⚠ netherton_hub.ink - has choice nesting errors
⚠ haxolottle_hub.ink - has missing knot targets and variable errors

story_design/ink/haxolottle_hub.ink

@@ -214,7 +214,7 @@ Haxolottle: Tell me the situation. What's the immediate threat?
 
 + [Equipment failure in critical situation]
     Haxolottle: *contacts Dr. Chen on second channel* Chen, I need you. Equipment failure, active operation.
-    Haxolottle: Agent {player_name}, Chen is on comms now. Walk them through the problem.
+    Haxolottle: Agent {player_name()}, Chen is on comms now. Walk them through the problem.
     -> equipment_crisis_support
 
 === crisis_solution_planning ===
@@ -265,7 +265,7 @@ Haxolottle: Route to waypoint Bravo: *provides detailed navigation*
 
 Haxolottle: I've got eyes on security feeds. I'll guide you around patrol patterns.
 
-Haxolottle: {player_name}—*firm but caring*—you've got this. I'm with you every step. Move now.
+Haxolottle: {player_name()}—*firm but caring*—you've got this. I'm with you every step. Move now.
 
 #emergency_extraction_active
 -> END
@@ -399,7 +399,7 @@ Haxolottle: *urgent typing* Okay. Either my feeds are compromised or ENTROPY cha
 Haxolottle: Recommend trusting your eyes over my monitors. Proceed with extreme caution. I'm investigating the discrepancy.
 
 {npc_haxolottle_friendship_level >= 50:
-    Haxolottle: *concerned* And {player_name}? Be careful. If my intel is wrong, you're more exposed than we thought.
+    Haxolottle: *concerned* And {player_name()}? Be careful. If my intel is wrong, you're more exposed than we thought.
     ~ npc_haxolottle_friendship_level += 5
 }
 
@@ -524,7 +524,7 @@ Haxolottle: Before we do the formal debrief—are you actually okay? Not the pro
     -> debrief_completion
 
 + [Downplay it professionally]
-    Haxolottle: *sees through it* Agent {player_name}. I watched that mission. It was rough. Don't minimize it.
+    Haxolottle: *sees through it* Agent {player_name()}. I watched that mission. It was rough. Don't minimize it.
     Haxolottle: Acknowledging difficulty isn't weakness. It's accurate assessment.
     -> rough_mission_debrief
 
@@ -546,7 +546,7 @@ Haxolottle: Debrief complete. After-action report will go to Netherton and opera
     ~ total_missions_completed += 1
 }
 
-Haxolottle: You did good work, {player_name}. Really.
+Haxolottle: You did good work, {player_name()}. Really.
 
 #debrief_complete
 -> haxolottle_main_hub
@@ -632,5 +632,3 @@ Haxolottle: And honestly? A lot of it is managing stress. Yours and ours. Keepin
     ~ npc_haxolottle_friendship_level += 10
     #handler_training_offered
     -> haxolottle_main_hub
-
-=== END

story_design/ink/haxolottle_ongoing_conversations.ink

@@ -659,7 +659,7 @@ Haxolottle: *slight smile* Thank you. I know that, intellectually. Regulation 91
 
 Haxolottle: Doesn't make it easier. But it helps to hear it from someone who understands. Someone who's been there.
 
-Haxolottle: You're a good person, Agent {player_name}. I'm glad we're working together.
+Haxolottle: You're a good person, Agent {player_name()}. I'm glad we're working together.
 
 ~ npc_haxolottle_friendship_level += 15
 -> phase_2_hub
@@ -951,7 +951,7 @@ Haxolottle: But it's worth checking in with yourself. "Is this useful vigilance
 
 {
     - npc_haxolottle_conversations_had >= 5 and npc_haxolottle_friendship_level >= 40:
-        Haxolottle: I really appreciate these talks, Agent {player_name}. Makes the work feel less isolating.
+        Haxolottle: I really appreciate these talks, Agent {player_name()}. Makes the work feel less isolating.
     - else:
         Haxolottle: Alright. Back to the mission. Talk later.
 }

story_design/ink/netherton_hub.ink

@@ -220,7 +220,7 @@ Netherton: Questions?
 
 + [I'm ready to proceed]
     Netherton: Excellent. *hands you mission packet* Review the details. Brief with Dr. Chen for equipment. Haxolottle will coordinate deployment.
-    Netherton: Agent {player_name}—*direct look*—execute this cleanly. We're counting on you.
+    Netherton: Agent {player_name()}—*direct look*—execute this cleanly. We're counting on you.
     #mission_briefing_complete
     -> netherton_main_hub
 
@@ -350,5 +350,3 @@ Netherton: Training opportunities. What areas interest you?
     Netherton: Dr. Chen runs technical workshops. I'll arrange access. They'll be pleased to have an agent interested in deep technical capability.
     ~ professional_reputation += 2
     -> netherton_main_hub
-
-=== END

story_design/ink/netherton_ongoing_conversations.ink

@@ -84,11 +84,11 @@ EXTERNAL current_mission_id()           // LOCAL - Current mission identifier
 
 {
     - total_missions_completed == 1:
-        Netherton: Agent {player_name}. I have a few minutes available. Is there something you wish to discuss?
+        Netherton: Agent {player_name()}. I have a few minutes available. Is there something you wish to discuss?
     - npc_netherton_respect >= 60:
         Netherton: Agent. Your performance has been noted. What can I address for you today?
     - else:
-        Netherton: Agent {player_name}. You have questions?
+        Netherton: Agent {player_name()}. You have questions?
 }
 
 + {not npc_netherton_discussed_handbook} [Ask about the Field Operations Handbook]
@@ -385,11 +385,11 @@ Netherton: Specific areas for development will be addressed in formal performanc
 
 {
     - npc_netherton_respect >= 70:
-        Netherton: Agent {player_name}. Your continued excellent performance has been noted. What do you wish to discuss?
+        Netherton: Agent {player_name()}. Your continued excellent performance has been noted. What do you wish to discuss?
     - npc_netherton_respect >= 60:
         Netherton: Agent. I have time for a brief discussion.
     - else:
-        Netherton: Agent {player_name}. What requires attention?
+        Netherton: Agent {player_name()}. What requires attention?
 }
 
 + {not npc_netherton_discussed_difficult_decisions} [Ask about making difficult command decisions]
@@ -771,11 +771,11 @@ Netherton: But that's the price of command. Acceptable trade for the impact I ca
 
 {
     - npc_netherton_respect >= 80:
-        Netherton: Agent {player_name}. *almost warmth* Your continued excellence is appreciated. What's on your mind?
+        Netherton: Agent {player_name()}. *almost warmth* Your continued excellence is appreciated. What's on your mind?
     - npc_netherton_respect >= 70:
         Netherton: Agent. I have time for a substantive discussion.
     - else:
-        Netherton: Agent {player_name}. What do you need?
+        Netherton: Agent {player_name()}. What do you need?
 }
 
 + {not npc_netherton_discussed_weight_of_command and npc_netherton_respect >= 75} [Ask about the weight of command]
@@ -1212,9 +1212,9 @@ Netherton: Though I sometimes suspect I only believe that because accepting the
 
 {
     - npc_netherton_respect >= 90:
-        Netherton: {player_name}. *uses first name, extremely rare* We should talk.
+        Netherton: {player_name()}. *uses first name, extremely rare* We should talk.
     - npc_netherton_respect >= 80:
-        Netherton: Agent {player_name}. I value your perspective. What's on your mind?
+        Netherton: Agent {player_name()}. I value your perspective. What's on your mind?
     - else:
         Netherton: Agent. I have time.
 }
@@ -1592,7 +1592,7 @@ Netherton: The fact that you understand that—that protocols are tools, not rep
 
 {
     - npc_netherton_respect >= 70:
-        Netherton: Acceptable performance continues, Agent {player_name}. Dismissed.
+        Netherton: Acceptable performance continues, Agent {player_name()}. Dismissed.
     - npc_netherton_respect >= 55:
         Netherton: Carry on, Agent.
     - else:
@@ -1620,7 +1620,7 @@ Netherton: The fact that you understand that—that protocols are tools, not rep
 
 {
     - npc_netherton_respect >= 85:
-        Netherton: Agent {player_name}. *rare warmth* Your service is valued. Genuinely.
+        Netherton: Agent {player_name()}. *rare warmth* Your service is valued. Genuinely.
     - npc_netherton_respect >= 75:
         Netherton: Excellent work continues. Carry on, Agent.
     - else:
@@ -1634,7 +1634,7 @@ Netherton: The fact that you understand that—that protocols are tools, not rep
 
 {
     - npc_netherton_respect >= 95:
-        Netherton: {player_name}. *uses first name* It's been an honor working with you. Until next time.
+        Netherton: {player_name()}. *uses first name* It's been an honor working with you. Until next time.
     - npc_netherton_respect >= 85:
         Netherton: Thank you for your time, Agent. And for your service.
     - else: