fix(plan): add tier hydration and improve architecture review output (#10938)

## Summary

This PR fixes issue #10878 where architecture reviews were truncated because the regex pattern for parsing file output would stop at the first ``` encountered in the Markdown report.

## Changes

- Change file delimiters from ``` to >>>>>>>/<<<<<<< to avoid Markdown conflicts
- Add tier hydration before strategize phase in plan_executor.py
- Increase max_tokens to 16384 in llm_actors.py for longer outputs
- Increase context_max_tokens_hot from 16000 to 32000 in settings.py
- Fix get_hot_view → get_hot_fragments in strategy_actor.py and plan_executor.py
- Add opencode to skip directories in context_tier_hydrator.py
- Change sandbox output location to plan-output/ directory in plan.py
- Add get_context_summary stub method to acms_service.py

## Testing

Run architecture review action and verify the output report is complete with all sections.

Reviewed-on: #10938

.gitignore

@@ -183,3 +183,6 @@ agents-test
 
 # Generated test reports (CI artifacts) — build artifacts, not to be committed
 test_reports/
+
+# Auto-added by CleverAgents plan executor
+plan-output/