fix(web): Address review findings for M4-LLM integration

- Sanitize user-facing error messages (no raw API/DB errors)
- Remove dead try/catch from Chat.tsx handleSendMessage
- Add onError callback for persistence errors in useChat
- Add console.error logging to loadConversation
- Guard minimize/toggleMinimize against closed overlay state
- Improve error dedup bucketing for non-DOMException errors
- Add tests: non-Error throws, updateConversation failure,
  minimize/toggleMinimize guards

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

apps/web/src/hooks/useChatOverlay.ts

@@ -83,7 +83,12 @@ function saveState(
   try {
     window.localStorage.setItem(STORAGE_KEY, JSON.stringify(state));
   } catch (error) {
-    const errorName = error instanceof DOMException ? error.name : "UnknownError";
+    const errorName =
+      error instanceof DOMException
+        ? error.name
+        : error instanceof Error
+          ? error.constructor.name
+          : "UnknownError";
     console.warn("Failed to save chat overlay state to localStorage:", error);
 
     if (onStorageError && !notifiedErrors.has(errorName)) {
@@ -119,7 +124,7 @@ export function useChatOverlay(options: UseChatOverlayOptions = {}): UseChatOver
   }, []);
 
   const minimize = useCallback(() => {
-    setState((prev) => ({ ...prev, isMinimized: true }));
+    setState((prev) => (prev.isOpen ? { ...prev, isMinimized: true } : prev));
   }, []);
 
   const expand = useCallback(() => {
@@ -134,7 +139,7 @@ export function useChatOverlay(options: UseChatOverlayOptions = {}): UseChatOver
   }, []);
 
   const toggleMinimize = useCallback(() => {
-    setState((prev) => ({ ...prev, isMinimized: !prev.isMinimized }));
+    setState((prev) => (prev.isOpen ? { ...prev, isMinimized: !prev.isMinimized } : prev));
   }, []);
 
   return {