Add per-module log level overrides for staging/production

Support LOG_LEVEL_{MODULE} env vars (GAME, AI, HANDLERS, ROOM, AUTH,
STORES) to override the global log level for specific modules. Active
overrides are logged at startup. Includes staging/production presets
in .env.example files and a V3.18 stub doc for PostgreSQL storage
efficiency investigation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -20,6 +20,24 @@ DEBUG=false
 # Logging level: DEBUG, INFO, WARNING, ERROR, CRITICAL
 LOG_LEVEL=INFO
 
+# Per-module log level overrides (optional)
+# These override LOG_LEVEL for specific modules.
+# LOG_LEVEL_GAME=DEBUG       # Core game logic
+# LOG_LEVEL_AI=DEBUG         # AI decisions (very verbose at DEBUG)
+# LOG_LEVEL_HANDLERS=DEBUG   # WebSocket message handlers
+# LOG_LEVEL_ROOM=DEBUG       # Room/lobby management
+# LOG_LEVEL_AUTH=DEBUG       # Auth stack (auth, routers.auth, services.auth_service)
+# LOG_LEVEL_STORES=DEBUG     # Database/Redis operations
+
+# --- Preset examples ---
+# Staging (debug game logic, quiet everything else):
+#   LOG_LEVEL=INFO
+#   LOG_LEVEL_GAME=DEBUG
+#   LOG_LEVEL_AI=DEBUG
+#
+# Production (minimal logging):
+#   LOG_LEVEL=WARNING
+
 # Environment name (development, staging, production)
 ENVIRONMENT=development