fix: const redeclaration bug + bare ctx references

- Remove duplicate const TILE_HEIGHT/TILE_WIDTH in player.js and game.js
- Use var TILE_HEIGHT_PLAYER in player.js to avoid collision
- Fix bare ctx → this.ctx in monster render
- Fix ctx = this.ctx → const ctx = this.ctx in NPC render

This was causing a SyntaxError that prevented the entire game from loading.

frontend/js/game.js

@@ -1,8 +1,5 @@
 // game.js — Main Game Loop
 
-const TILE_WIDTH = 64;
-const TILE_HEIGHT = 32;
-
 class Game {
     constructor() {
         this.canvas = document.getElementById('game-canvas');
@@ -336,7 +333,7 @@ class Game {
                 class_master: '#8a4a8a',
                 innkeeper: '#8a8a4a'
             };
-            ctx = this.ctx;
+            const ctx = this.ctx;
             ctx.fillStyle = colors[npc.type] || '#666';
             ctx.fillRect(drawX - 5, drawY + TILE_HEIGHT/2 - 15, 10, 12);
             ctx.fillStyle = '#e0b890';
@@ -374,9 +371,9 @@ class Game {
             this.ctx.fillStyle = '#666';
             this.ctx.fillRect(drawX - 6, drawY + TILE_HEIGHT/2 - 10, 12, 8);
             this.ctx.fillStyle = '#555';
-            ctx.beginPath();
-            ctx.arc(drawX, drawY + TILE_HEIGHT/2 - 12, 5, 0, Math.PI * 2);
-            ctx.fill();
+            this.ctx.beginPath();
+            this.ctx.arc(drawX, drawY + TILE_HEIGHT/2 - 12, 5, 0, Math.PI * 2);
+            this.ctx.fill();
             
             // Eyes (red)
             this.ctx.fillStyle = '#ff3333';