fix(web): enable noUncheckedIndexedAccess in tsconfig

Enable the TypeScript strict flag `noUncheckedIndexedAccess` which ensures
that indexed access (arrays, Record types) includes `| undefined` in the
result type, catching potential runtime errors at compile time.

Current state:
- 493 pre-existing type errors (before this flag)
- ~234 additional errors introduced by this flag
- Errors should be fixed progressively, prioritizing features/ and services/
- Pattern: use optional chaining (value?.) or null checks (if (value != null))

This flag was previously commented out with a TODO. Enabling it now ensures
new code is written safely, even as existing errors are addressed over time.

Addresses audit finding: debt item 10 (TypeScript strictness).

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/web/tsconfig.json

@@ -29,7 +29,7 @@
     "noUnusedParameters": true,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
-    // "noUncheckedIndexedAccess": true, // TODO: Enable progressively - requires fixing 200+ array/object access checks
+    "noUncheckedIndexedAccess": true, // Enabled in audit remediation C12 — adds ~234 errors on top of 493 pre-existing; fix progressively
     "noImplicitOverride": true,
     "baseUrl": ".",
     "paths": {