feat: port Java Supersonic bot framework and cash game bots to Rust

Framework (holdem_core::game::strategy):
- HandAnalyzer: 15 hand analysis methods (overpair, flush draw, OESD, outs, etc.)
- HandHelper: 14 board texture and hand strength methods (Kill Phil grouping, etc.)
- ActionRecorder: per-street action tracking with player filtering
- StrategyContext: read-only game state snapshot with position/pot odds helpers
- Strategy trait + ModularStrategy: composite pattern with 3 voting modes
  (FirstApplicable, Democratic, Random)

Cash Game Bots (holdem_bots crate — private, exclude from public mirrors):
- PostFlopStrategy: shared postflop logic using hand strength approximation
- BigStackBot: NL cash strategy for stack > 25 BB (preflop + postflop)
- ShortStackBot: NL cash strategy for stack ≤ 25 BB (preflop + postflop)
- Full preflop decision trees ported from Java Supersonic framework

Repository restructuring:
- Created holdem_bots crate with feature-gated dependency from holdem_sim
- Added game::strategy module to holdem_core
- Cleaned up 4 unused evaluator stubs
- Moved plans/ to docs/, added proptest-regressions/ to .gitignore
- Added ARCHITECTURE_BOT_FRAMEWORK.md documentation

Tests: 58 new strategy tests + 17 bot tests (all passing)

.gitignore

@@ -8,3 +8,10 @@
 # OS
 .DS_Store
 Thumbs.db
+
+# Proptest regressions (auto-generated)
+proptest-regressions/
+
+# Private bot strategies — exclude from public mirrors
+# Uncomment the following lines when pushing to public repositories:
+# holdem_bots/