feat: Implement Phase 5 Quest System (100% complete)

Add YAML-driven quest system with context-aware offering:

Core Implementation:
- Quest data models (Quest, QuestObjective, QuestReward, QuestTriggers)
- QuestService for YAML loading and caching
- QuestEligibilityService with level, location, and probability filtering
- LoreService stub (MockLoreService) ready for Phase 6 Weaviate integration

Quest Content:
- 5 example quests across difficulty tiers (2 easy, 2 medium, 1 hard)
- Quest-centric design: quests define their NPC givers
- Location-based probability weights for natural quest offering

AI Integration:
- Quest offering section in npc_dialogue.j2 template
- Response parser extracts [QUEST_OFFER:quest_id] markers
- AI naturally weaves quest offers into NPC conversations

API Endpoints:
- POST /api/v1/quests/accept - Accept quest offer
- POST /api/v1/quests/decline - Decline quest offer
- POST /api/v1/quests/progress - Update objective progress
- POST /api/v1/quests/complete - Complete quest, claim rewards
- POST /api/v1/quests/abandon - Abandon active quest
- GET /api/v1/characters/{id}/quests - List character quests
- GET /api/v1/quests/{quest_id} - Get quest details

Frontend:
- Quest tracker sidebar with HTMX integration
- Quest offer modal for accept/decline flow
- Quest detail modal for viewing progress
- Combat service integration for kill objective tracking

Testing:
- Unit tests for Quest models and serialization
- Integration tests for full quest lifecycle
- Comprehensive test coverage for eligibility service

Documentation:
- Reorganized docs into /docs/phases/ structure
- Added Phase 5-12 planning documents
- Updated ROADMAP.md with new structure

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

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

api/app/models/character.py

@@ -66,6 +66,8 @@ class Character:
 
     # Quests and exploration
     active_quests: List[str] = field(default_factory=list)
+    completed_quests: List[str] = field(default_factory=list)
+    quest_states: Dict[str, Dict] = field(default_factory=dict)  # quest_id -> CharacterQuestState.to_dict()
     discovered_locations: List[str] = field(default_factory=list)
     current_location: Optional[str] = None  # Set to origin starting location on creation
 
@@ -378,6 +380,8 @@ class Character:
             "equipped": {slot: item.to_dict() for slot, item in self.equipped.items()},
             "gold": self.gold,
             "active_quests": self.active_quests,
+            "completed_quests": self.completed_quests,
+            "quest_states": self.quest_states,
             "discovered_locations": self.discovered_locations,
             "current_location": self.current_location,
             "npc_interactions": self.npc_interactions,
@@ -467,6 +471,8 @@ class Character:
             equipped=equipped,
             gold=data.get("gold", 0),
             active_quests=data.get("active_quests", []),
+            completed_quests=data.get("completed_quests", []),
+            quest_states=data.get("quest_states", {}),
             discovered_locations=data.get("discovered_locations", []),
             current_location=data.get("current_location"),
             npc_interactions=data.get("npc_interactions", {}),