Save character inventory and auto-save on server shutdown

[FirebrickRed]

Priority: HIGH
Status: TODO
Related: #25 (Class Resources), #26 (Spell Slots)

Problem

Character data is not fully persisted to YAML. Currently saves basic info (name, race, class, abilities, HP, AC) but missing:

• ❌ Equipment/inventory items
• ❌ Equipped armor and shield
• ❌ Class resources (Rage, Ki Points, Bardic Inspiration, etc.)
• ❌ Known spells and cantrips
• ❌ Current spell slot state (mentioned in code TODOs)
• ❌ Auto-save on server shutdown not implemented

Result: Players lose resources, spells, and items on server restart!

Acceptance Criteria

Equipment Persistence

• Save equipment list to YAML (item IDs and quantities)
• Save equipped armor ID
• Save equipped shield ID
• Load equipment on character load
• Re-equip armor/shield on load

Class Resources Persistence (Issue #25)

• Save class resources (name, current, max, recovery type)
• Load resources on character load

Spell Persistence

• Save known spells (spell names list)
• Save known cantrips (cantrip names list)
• Save current spell slots per level (not just max)
• Load all spell data on character load

Auto-Save System

• Hook into server shutdown event
• Call CharacterSheetManager.saveAllCharacters() on shutdown
• Ensure all active characters are persisted
• Add periodic auto-save (optional: every 5 minutes?)

YAML Format Updates

Current format:

character_name: Bjorn
race: Human
class: Barbarian
# ... basic fields

New format:

character_name: Bjorn
race: Human
class: Barbarian
# ... existing fields ...

# NEW: Class resources
class_resources:
  - name: Rage
    current: 1
    max: 2
    recovery: LONG_REST

# NEW: Spells
known_spells:
  - Cure Wounds
  - Bless
known_cantrips:
  - Sacred Flame
  - Light

# NEW: Spell slots
spell_slots_current: [2, 1, 0, 0, 0, 0, 0, 0, 0]  # Current slots per level
spell_slots_max: [3, 2, 0, 0, 0, 0, 0, 0, 0]      # Max slots per level

# NEW: Equipment
equipment:
  - greataxe
  - leather_armor
  - explorers_pack
equipped_armor: leather_armor
equipped_shield: null

Technical Notes

• Update CharacterPersistenceLoader.saveCharacter() to save new fields
• Update CharacterSheet.loadFromData() to load new fields
• Use ClassResource serialization for resource data
• Consider adding lastSaved timestamp for debugging

Related Issues

• Issue Implement class resource system #25: Class resource system (now needs persistence) ✅
• Issue Implement spell slot progression system #26: Spell slot progression (current state needs saving)
• Issue Refactor character persistence to use DataManager pattern #28: Refactor to DataManager pattern (architectural cleanup - separate task)

Future Enhancements

• Periodic auto-save (every 5 minutes)
• Character backup system