Implement tile discarding, blocked doors, and correct corridor exits

- Updated TileDefinitions.js: Added 4-way exits to corridor_straight and corridor_steps (N/S y=3,4; E/W x=3,4).
- Updated DungeonGenerator.js: Added cancelPlacement() logic and onDoorBlocked callback.
- Updated GameRenderer.js: Implemented blockDoor() to visualize blocked passages, and improved isPlayerAdjacentToDoor.
- Updated UIManager.js: Added custom showModal/showConfirm and Discard button for tile placement.
- Updated main.js: Handled blocked door clicks and hooked up UI events.
- Updated GameEngine.js: Improved door adjacency checks.
- Updated CameraManager.js: Preserved camera rotation on centerOn.
- Added door1_blocked.png asset.

src/view/GameRenderer.js

@@ -601,6 +601,36 @@ export class GameRenderer {
         return false;
     }
 
+    blockDoor(exitData) {
+        if (!this.exitGroup || !exitData) return;
+
+        // Find the door mesh
+        let targetDoor = null;
+
+        for (const child of this.exitGroup.children) {
+            if (child.userData.isDoor) {
+                // Check if this door corresponds to the exitData
+                // exitData has x,y of one of the cells
+                for (const cell of child.userData.cells) {
+                    if (cell.x === exitData.x && cell.y === exitData.y) {
+                        targetDoor = child;
+                        break;
+                    }
+                }
+            }
+            if (targetDoor) break;
+        }
+
+        if (targetDoor) {
+            this.getTexture('/assets/images/dungeon1/doors/door1_blocked.png', (texture) => {
+                targetDoor.material.map = texture;
+                targetDoor.material.needsUpdate = true;
+                targetDoor.userData.isBlocked = true;
+                targetDoor.userData.isOpen = false; // Ensure strictly not open
+            });
+        }
+    }
+
     // ========== MANUAL PLACEMENT SYSTEM ==========
 
     enableDoorSelection(enabled) {
@@ -727,12 +757,31 @@ export class GameRenderer {
             });
         }
 
-        // 2. GROUND PROJECTION (Green/Red)
-        const projectionColor = isValid ? 0x00ff00 : 0xff0000;
+        // 2. GROUND PROJECTION (Green/Red/Blue)
+        const baseColor = isValid ? 0x00ff00 : 0xff0000;
+
+        // Calculate global exit positions
+        const exitKeys = new Set();
+        if (preview.variant && preview.variant.exits) {
+            preview.variant.exits.forEach(ex => {
+                const gx = x + ex.x;
+                const gy = y + ex.y;
+                exitKeys.add(`${gx},${gy}`);
+            });
+        }
+
         cells.forEach(cell => {
+            const key = `${cell.x},${cell.y}`;
+            let color = baseColor;
+
+            // If this cell is an exit, color it Blue
+            if (exitKeys.has(key)) {
+                color = 0x0000ff; // Blue
+            }
+
             const geometry = new THREE.PlaneGeometry(0.95, 0.95);
             const material = new THREE.MeshBasicMaterial({
-                color: projectionColor,
+                color: color,
                 transparent: true,
                 opacity: 0.5,
                 side: THREE.DoubleSide