Enable noUncheckedIndexedAccess

Tightens array and record indexing to surface missing-element bugs at
compile time. No call sites needed adjustment — existing code already
guarded or used .find / Map.get patterns.

Author: chapterjason

tsconfig.json

@@ -10,6 +10,7 @@
     "noFallthroughCasesInSwitch": true,
     "noImplicitOverride": true,
     "exactOptionalPropertyTypes": true,
+    "noUncheckedIndexedAccess": true,
     "isolatedModules": true,
     "esModuleInterop": true,
     "resolveJsonModule": true,