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/ChatInput.tsx

@@ -9,14 +9,19 @@ interface ChatInputProps {
   inputRef?: RefObject<HTMLTextAreaElement | null>;
 }
 
-export function ChatInput({ onSend, disabled, inputRef }: ChatInputProps) {
+export function ChatInput({ onSend, disabled, inputRef }: ChatInputProps): React.JSX.Element {
   const [message, setMessage] = useState("");
   const [version, setVersion] = useState<string | null>(null);
 
   // Fetch version from static version.json (generated at build time)
   useEffect(() => {
+    interface VersionData {
+      version?: string;
+      commit?: string;
+    }
+
     fetch("/version.json")
-      .then((res) => res.json())
+      .then((res) => res.json() as Promise<VersionData>)
       .then((data) => {
         if (data.version) {
           // Format as "version+commit" for full build identification
@@ -83,10 +88,10 @@ export function ChatInput({ onSend, disabled, inputRef }: ChatInputProps) {
             minHeight: "48px",
             maxHeight: "200px",
           }}
-          onInput={(e) => {
+          onInput={(e): void => {
             const target = e.target as HTMLTextAreaElement;
             target.style.height = "auto";
-            target.style.height = Math.min(target.scrollHeight, 200) + "px";
+            target.style.height = `${String(Math.min(target.scrollHeight, 200))}px`;
           }}
           aria-label="Message input"
           aria-describedby="input-help"
@@ -96,7 +101,7 @@ export function ChatInput({ onSend, disabled, inputRef }: ChatInputProps) {
         <div className="absolute bottom-2 right-2 flex items-center gap-2">
           <button
             onClick={handleSubmit}
-            disabled={disabled || !message.trim() || isOverLimit}
+            disabled={(disabled ?? !message.trim()) || isOverLimit}
             className="btn-primary btn-sm rounded-md"
             style={{
               opacity: disabled || !message.trim() || isOverLimit ? 0.5 : 1,