refactor(games): rework room lifecycle events and remove chess plugin

Consolidate room leave/delete event handling into RoomManager emitter,
remove redundant PLAYER_LEFT publishes from GameServer, and delete the
chess game plugin (board, types, tests) in favor of the new plugin
architecture. Add per-module CLAUDE.md files for leveling, guild-settings,
feature-flags, db, api, and panel to improve agent navigability.

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

shared/modules/guild-settings/CLAUDE.md

@@ -0,0 +1,10 @@
+# Guild Settings Module
+
+- `updateSetting()` uses a hardcoded `keyMap` to map friendly key names to DB columns. Use exact key names (e.g., `"studentRole"` not `"studentRoleId"`). Unknown keys throw `UserError`.
+- Type coercion per column: Discord IDs → BigInt automatically; `colorRoleIds` must be array; `featureOverrides` must be object; `moderationDmOnWarn` must be boolean; `moderationAutoTimeoutThreshold` must be number. Null values set columns to NULL.
+- **Caching:** `getGuildConfig()` (in `shared/lib/config.ts`) caches transformed settings for 60 seconds. Every mutation (`upsertSettings`, `updateSetting`, `addColorRole`, `removeColorRole`) calls `invalidateGuildConfigCache(guildId)` immediately.
+- If settings don't exist for a guild, the cache returns safe defaults — no errors thrown.
+- `featureOverrides` is a sparse `Record<string, boolean>` — no keys are predefined. Consumers must check key existence.
+- **No Discord validation:** The service does not verify that role/channel IDs actually exist in Discord. Invalid IDs are stored silently.
+- `addColorRole()` / `removeColorRole()` fetch the full settings, mutate the array in JS, then upsert — this is not atomic and can race under concurrent requests.
+- `terminalMessageId` and `terminalChannelId` are separate DB columns but grouped as `terminal: { channelId, messageId }` in the cached config. Setting one without the other can create orphaned data.