Fix chat.js BASE_PATH conflict: remove declaration entirely

var hoisting still conflicts with const from main.js.
chat.js now relies on BASE_PATH declared in main.js.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/static/js/chat.js

@@ -1,6 +1,5 @@
 // ── Chat Widget JavaScript ──
-// BASE_PATH is declared in main.js (loaded first on index.html)
-if (typeof BASE_PATH === 'undefined') var BASE_PATH = window.BASE_PATH || '';
+// NOTE: Uses BASE_PATH from main.js (loaded before this file on index.html)
 
 let chatSessionId = sessionStorage.getItem('chat_session');
 if (!chatSessionId) {