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/hooks/useChat.ts

@@ -209,7 +209,7 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
 
         // Add error message to chat
         const errorMessage: Message = {
-          id: `error-${Date.now()}`,
+          id: `error-${String(Date.now())}`,
           role: "assistant",
           content: `Error: ${errorMsg}`,
           createdAt: new Date().toISOString(),