feat(engine): harden review pipeline with strict scope, build retry, and E2E tests

Improve the plan→review→approve→merge agent pipeline:

- Harden verdict extraction with JSON block parsing and anchored regexes
- Consolidate legacy/new merger conflict APIs into thin deprecated wrappers
- Add configurable strict scope enforcement (strictScopeEnforcement setting)
- Add build retry with timeout to merger (buildRetryCount, buildTimeoutMs)
- Add handleChangesRequested to PrCommentHandler for review feedback loop
- Remove dead code: handleFsChange, processTaskChange, unused imports/fields
- Add E2E multi-verdict sequence tests for the full review pipeline
- Fix unused parameter warnings across engine and core packages

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/engine/src/runtimes/in-process-runtime.ts

@@ -460,7 +460,7 @@ export class InProcessRuntime
   /**
    * Record task completion in CentralCore.
    */
-  private async recordTaskCompletion(taskId: string, success: boolean): Promise<void> {
+  private async recordTaskCompletion(_taskId: string, success: boolean): Promise<void> {
     try {
       // Estimate duration (simplified - in reality, we'd track start time)
       const durationMs = 0; // Placeholder