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/MessageList.tsx

@@ -32,13 +32,18 @@ function parseThinking(content: string): { thinking: string | null; response: st
   // Remove thinking blocks from response
   const response = content.replace(thinkingRegex, "").trim();
 
+  const trimmedThinking = thinking.trim();
   return {
-    thinking: thinking.trim() || null,
+    thinking: trimmedThinking.length > 0 ? trimmedThinking : null,
     response,
   };
 }
 
-export function MessageList({ messages, isLoading, loadingQuip }: MessageListProps) {
+export function MessageList({
+  messages,
+  isLoading,
+  loadingQuip,
+}: MessageListProps): React.JSX.Element {
   return (
     <div className="space-y-6" role="log" aria-label="Chat messages">
       {messages.map((message) => (
@@ -50,7 +55,7 @@ export function MessageList({ messages, isLoading, loadingQuip }: MessageListPro
   );
 }
 
-function MessageBubble({ message }: { message: Message }) {
+function MessageBubble({ message }: { message: Message }): React.JSX.Element {
   const isUser = message.role === "user";
   const [copied, setCopied] = useState(false);
   const [thinkingExpanded, setThinkingExpanded] = useState(false);
@@ -122,7 +127,7 @@ function MessageBubble({ message }: { message: Message }) {
                 backgroundColor: "rgb(var(--surface-2))",
                 color: "rgb(var(--text-muted))",
               }}
-              title={`Prompt: ${message.promptTokens?.toLocaleString() || "0"} tokens, Completion: ${message.completionTokens?.toLocaleString() || "0"} tokens`}
+              title={`Prompt: ${message.promptTokens?.toLocaleString() ?? "0"} tokens, Completion: ${message.completionTokens?.toLocaleString() ?? "0"} tokens`}
             >
               {formatTokenCount(message.totalTokens)} tokens
             </span>
@@ -238,7 +243,7 @@ function MessageBubble({ message }: { message: Message }) {
   );
 }
 
-function LoadingIndicator({ quip }: { quip?: string | null }) {
+function LoadingIndicator({ quip }: { quip?: string | null }): React.JSX.Element {
   return (
     <div className="flex gap-4 message-animate" role="status" aria-label="AI is typing">
       {/* Avatar */}