refactor: remove ~275 lines of dead code and enable stricter tsconfig

- Delete unused src/cli/ui.ts, remove zod dependency, drop 4 dead functions (logError, handleToolError, getRetryDelay, displayTimingSummary)
- Remove 8 unused types/interfaces and 3 duplicate formatting utils from audit/utils.ts
- Narrow export surface: make 7 message-handler functions private, remove unused audit re-exports, unexport AgentDefinition and path constants
- Remove unused runClaudePrompt params (sessionMetadata, attemptNumber) and update caller
- Enable tsconfig noUnusedLocals, noUnusedParameters, noImplicitReturns, noImplicitOverride, noFallthroughCasesInSwitch

tsconfig.json

@@ -33,11 +33,11 @@
     "exactOptionalPropertyTypes": true,
 
     // Style Options
-    // "noImplicitReturns": true,
-    // "noImplicitOverride": true,
-    // "noUnusedLocals": true,
-    // "noUnusedParameters": true,
-    // "noFallthroughCasesInSwitch": true,
+    "noImplicitReturns": true,
+    "noImplicitOverride": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true,
     // "noPropertyAccessFromIndexSignature": true,
 
     // Recommended Options