fix: Resolve all ESLint errors and warnings in web package

Fixes all 542 ESLint problems in the web package to achieve 0 errors and 0 warnings.

Changes:
- Fixed 144 issues: nullish coalescing, return types, unused variables
- Fixed 118 issues: unnecessary conditions, type safety, template literals
- Fixed 79 issues: non-null assertions, unsafe assignments, empty functions
- Fixed 67 issues: explicit return types, promise handling, enum comparisons
- Fixed 45 final warnings: missing return types, optional chains
- Fixed 25 typecheck-related issues: async/await, type assertions, formatting
- Fixed JSX.Element namespace errors across 90+ files

All Quality Rails violations resolved. Lint and typecheck both pass with 0 problems.

Files modified: 118 components, tests, hooks, and utilities

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/components/chat/Chat.tsx

@@ -96,13 +96,13 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
 
   // Expose methods to parent via ref
   useImperativeHandle(ref, () => ({
-    loadConversation: async (conversationId: string) => {
+    loadConversation: async (conversationId: string): Promise<void> => {
       await loadConversation(conversationId);
     },
-    startNewConversation: (projectId?: string | null) => {
+    startNewConversation: (projectId?: string | null): void => {
       startNewConversation(projectId);
     },
-    getCurrentConversationId: () => conversationId,
+    getCurrentConversationId: (): string | null => conversationId,
   }));
 
   const scrollToBottom = useCallback(() => {
@@ -130,7 +130,7 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
 
   // Global keyboard shortcut: Ctrl+/ to focus input
   useEffect(() => {
-    const handleKeyDown = (e: KeyboardEvent) => {
+    const handleKeyDown = (e: KeyboardEvent): void => {
       if ((e.ctrlKey || e.metaKey) && e.key === "/") {
         e.preventDefault();
         inputRef.current?.focus();