feat: add configuration package with YAML loading and defaults

Add config package that loads game settings from YAML files with
sensible defaults for server, game, combat, dungeon, and backup
settings. Includes config.yaml with all defaults documented.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.yaml

@@ -0,0 +1,44 @@
+# Catacombs Configuration
+# All values shown are defaults. Uncomment and modify as needed.
+
+server:
+  # SSH port for game client connections
+  ssh_port: 2222
+  # HTTP port for web interface
+  http_port: 8080
+
+game:
+  # Seconds allowed per player turn
+  turn_timeout_sec: 5
+  # Maximum players per game session
+  max_players: 4
+  # Maximum dungeon floors
+  max_floors: 20
+  # Cooperative play bonus multiplier
+  coop_bonus: 0.10
+  # Maximum items a player can carry
+  inventory_limit: 10
+  # Number of skill uses per floor
+  skill_uses: 3
+
+combat:
+  # Probability of successfully fleeing combat
+  flee_chance: 0.50
+  # Monster stat scaling per floor
+  monster_scaling: 1.15
+  # HP reduction when playing solo
+  solo_hp_reduction: 0.50
+
+dungeon:
+  # Map dimensions in tiles
+  map_width: 60
+  map_height: 20
+  # Room count range per floor
+  min_rooms: 5
+  max_rooms: 8
+
+backup:
+  # Minutes between automatic backups
+  interval_min: 60
+  # Directory for backup files
+  dir: "./data/backup"