fix: prevent CDN from caching 404 responses for static assets

- add_no_cache_headers now only applies long-cache headers to 2xx responses
- non-2xx static responses (e.g. 404) get no-cache to prevent CDN from
  caching error pages (which was the root cause of office.hyacinth.im
  failing to load - Cloudflare cached a 404 for phaser.js for 2.7 days)
- add version cache-bust param to phaser.js script tag (matching all
  other static assets)

backend/app.py

@@ -109,10 +109,11 @@ def _require_asset_editor_auth():
 def add_no_cache_headers(response):
     """Apply cache policy by path:
     - HTML/API/state: no-cache (always fresh)
-    - /static assets: long cache (filenames are versioned with ?v=VERSION_TIMESTAMP)
+    - /static assets (2xx only): long cache (filenames are versioned with ?v=VERSION_TIMESTAMP)
+    - /static assets (non-2xx, e.g. 404): no-cache to prevent CDN from caching errors
     """
     path = (request.path or "")
-    if path.startswith('/static/'):
+    if path.startswith('/static/') and 200 <= response.status_code < 300:
         response.headers["Cache-Control"] = "public, max-age=31536000, immutable"
         response.headers.pop("Pragma", None)
         response.headers.pop("Expires", None)

frontend/index.html

@@ -1259,7 +1259,7 @@
         <button id="lang-btn-cn" onclick="setUILanguage('zh')" style="padding:8px 10px; font-family:ArkPixel,monospace; font-size:13px; cursor:pointer; border:2px solid #333; border-radius:5px; background:#333; color:#fff;">CN</button>
     </div>
 
-    <script src="/static/vendor/phaser-3.80.1.min.js"></script>
+    <script src="/static/vendor/phaser-3.80.1.min.js?v={{VERSION_TIMESTAMP}}"></script>
     <script>
         // 简易中英文切换
         let uiLang = localStorage.getItem('uiLang') || 'en';
@@ -4605,8 +4605,8 @@ function toggleBrokerPanel() {
                             typewriterText = '';
                             typewriterIndex = 0;
                         }
-                        }
-                    } catch (err) {
+                    }
+                } catch (err) {
                         console.error('fetchStatus apply error', err);
                         typewriterTarget = '状态更新异常，正在恢复...';
                         typewriterText = '';