feat: simulation resilience + flock_bot raise safety + trait extensions

- simulation.rs: RaiseBelowMinimum/InsufficientChips now skip hand
  instead of crashing entire simulation. Hands skipped are NOT counted
  in total_hands (accurate player stats).
- flock_bot.rs: Premium preflop raise falls back to Call when stack
  cannot afford minimum raise, preventing illegal AllIn edge cases.
- Added shutdown(), showdown_event() trait methods to HoldemPlayer.
- Added external_id, table_id to GameInfo/PlayerInfo.
- Strategy trait: added save_state() for graceful profile persistence.

.gitignore

@@ -12,3 +12,6 @@ Thumbs.db
 # Proptest regressions (auto-generated)
 proptest-regressions/
 
+
+# Agent notes
+AGENTS.md