feat(room-layout): Implement new grid-based room layout system with critical bug fixes

- Add grid unit constants (5x4 tiles) to constants.js
- Create comprehensive grid conversion helper functions
- Implement 4-direction room positioning (N/S/E/W) with breadth-first algorithm
- Add door placement functions with CRITICAL fixes:
  * Negative modulo fix: ((sum % 2) + 2) % 2 for deterministic placement
  * Asymmetric alignment fix: single-door rooms align with multi-door rooms
  * Consistent grid alignment using Math.floor() for negative coordinates
- Rewrite calculateRoomPositions to support variable room sizes
- Update createDoorSpritesForRoom to use new placement system
- Store room dimensions globally for cross-system access

This implements the comprehensive room layout redesign as specified in
planning_notes/new_room_layout with all critical fixes from review2.

Addresses: Variable room sizes, proper door alignment, and grid-based positioning

js/utils/constants.js

@@ -2,6 +2,17 @@
 export const TILE_SIZE = 32;
 export const DOOR_ALIGN_OVERLAP = 32 * 3;
 export const GRID_SIZE = 32;
+
+// Grid unit system constants for room layout
+// Grid units are the base stacking size for rooms
+export const GRID_UNIT_WIDTH_TILES = 5;    // 5 tiles wide
+export const GRID_UNIT_HEIGHT_TILES = 4;   // 4 tiles tall (stacking area)
+export const VISUAL_TOP_TILES = 2;         // Top 2 rows are visual wall overlay
+
+// Calculated grid unit sizes in pixels
+export const GRID_UNIT_WIDTH_PX = GRID_UNIT_WIDTH_TILES * TILE_SIZE;    // 160px
+export const GRID_UNIT_HEIGHT_PX = GRID_UNIT_HEIGHT_TILES * TILE_SIZE;  // 128px
+
 export const MOVEMENT_SPEED = 150;
 export const RUN_SPEED_MULTIPLIER = 1.5; // Speed multiplier when holding shift
 export const RUN_ANIMATION_MULTIPLIER = 1.5; // Animation speed multiplier when holding shift