Document retry config location and verify planning mode logic

Add documentation for retry configuration in planning mode:
- Document retry settings in .g3.toml under [agent] section
- Note RetryConfig implementation in g3-core/src/retry.rs
- Clarify hardcoded vs config-based retry values

Verify existing retry loop and coach feedback parsing:
- Confirm execute_with_retry() handles recoverable errors
- Document feedback extraction source priority order
- Provide manual verification steps for testing

g3-plan/completed_todo_2025-12-11_14-55-22.md

@@ -0,0 +1,16 @@
+# Planning Mode Verification Tasks
+
+## 1. Document Retry Configuration Location
+- [x] Add coach and player retry config examples to config.example.toml
+- [x] Document the relationship between config file settings and RetryConfig::planning()
+
+## 2. Verify Retry Loop Functionality
+- [x] Review retry logic implementation (already done - looks correct)
+- [x] Document verification findings
+
+## 3. Verify Coach Response Parsing
+- [x] Review feedback extraction implementation (already done - looks correct)
+- [x] Document verification findings
+
+## 4. Optional: Add Integration Test
+- [x] Create integration test for retry + feedback extraction flow in g3-planner/tests/