feat: request detailed reviewer guidance from cycle 3

When a run is about to start its 3rd cycle, the host review bundle asks
Codex to supply a step-by-step implementation plan via the new decision
field implementationGuidance, which is injected into the executor fix
prompt (with re-sent plan context) so the executor can converge faster.

- Add DETAILED_GUIDANCE_CYCLE_THRESHOLD and bundle signal in reviewWorkflow
- Add optional detailedGuidanceRequested/reviewerInstructions to the bundle
- Add optional implementationGuidance to HostDecisionV1 (validated, <=20000 chars)
- Inject guidance section and re-send plan/criteria on marked fix cycles
- Cover with integration, executor, and config validation tests

src/workflow-executor.ts

@@ -314,8 +314,15 @@ ${plan.verificationCommands.map((cmd) => `  ${cmd.join(" ")}`).join("\n")}
 ${getSafetyConstraints(opts.vcsKind)}`;
   }
 
-  return `# Fix Request: ${plan.title}
+  const hasDetailedGuidance = acceptedFindings.includes("## Detailed Implementation Guidance");
+  const planContext = hasDetailedGuidance
+    ? `\n## Plan\n\n${plan.planMarkdown}\n\n## Acceptance Criteria\n\n${plan.acceptanceCriteria
+        .map((c, i) => `  ${i + 1}. ${c}`)
+        .join("\n")}\n`
+    : "";
 
+  return `# Fix Request: ${plan.title}
+${planContext}
 The code review found the following issues that must be fixed:
 
 ${acceptedFindings}