Add SQLite persistence, per-player NPC attitude system, character creation, and combat

- Add trait-based DB layer (db.rs) with SQLite backend for easy future swapping
- Player state persisted to SQLite: stats, inventory, equipment, room position
- Returning players skip chargen and resume where they left off
- Replace boolean hostile flag with 5-tier attitude system (friendly/neutral/wary/aggressive/hostile)
- Per-player NPC attitudes stored in DB, shift on kills with faction propagation
- Add character creation flow (chargen.rs) with data-driven races and classes from TOML
- Add turn-based combat system (combat.rs) with XP, leveling, and NPC respawn
- Add commands: take, drop, inventory, equip, use, examine, talk, attack, flee, stats
- Add world data: 5 races, 4 classes, hostile NPCs (rat, thief), new items

Made-with: Cursor

world/town/npcs/rat.toml

@@ -0,0 +1,11 @@
+name = "Giant Rat"
+description = "A mangy rat the size of a small dog. Its eyes gleam with feral hunger."
+room = "town:cellar"
+base_attitude = "hostile"
+respawn_secs = 60
+
+[combat]
+max_hp = 25
+attack = 6
+defense = 2
+xp_reward = 15