fix: Replace static m_botReleaseTimes with per-bot storage to prevent race condition

Fixes a thread safety issue where multiple bots dying in battlegrounds
simultaneously would corrupt the shared static unordered_map, causing
segmentation faults.

Changes:
- Remove: static m_botReleaseTimes map from AutoReleaseSpiritAction
- Add: bgReleaseAttemptTime member to PlayerbotAI (per-bot storage)
- Update: All references to use per-bot storage instead of static map

Why this fixes the crash:
- Each PlayerbotAI instance is accessed by only one map update thread
- No cross-thread access to shared data structures
- No mutex/locking required - thread-safe by design
- Automatic cleanup when bot is destroyed

Thread-safe solution: Per-bot state eliminates race conditions without
performance overhead.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/PlayerbotAI.h

@@ -601,6 +601,7 @@ public:
     NewRpgInfo rpgInfo;
     NewRpgStatistic rpgStatistic;
     std::unordered_set<uint32> lowPriorityQuest;
+    time_t bgReleaseAttemptTime = 0;
 
     // Schedules a callback to run once after <delayMs> milliseconds.
     void AddTimedEvent(std::function<void()> callback, uint32 delayMs);