docs: rename CLAUDE.md to AGENTS.md across the project

shared/db/AGENTS.md

@@ -0,0 +1,40 @@
+# Database Layer
+
+## Column Types
+- **Bigint** (`mode: 'bigint'`): All Discord snowflake IDs (`userId`, `guildId`, `roleId`, `channelId`), currency amounts (`balance`, `xp`, transaction `amount`, item `price`, inventory `quantity`). Use `0n` BigInt literals, never `Number()`.
+- **Integer**: Small counts and internal IDs — `level`, `daily_streak`, `progress`, `reward_amount` in lootdrops, auto-increment `serial('id')` for items.
+
+## Composite Primary Keys
+- `inventory(userId, itemId)` — one stack per user per item
+- `userQuests(userId, questId)` — one assignment per user per quest
+- `userTimers(userId, type, key)` — one timer per user per type/key combo
+
+## Constraints
+- `inventory.quantity > 0` check constraint — never store zero-quantity rows
+- `classes.name` and `items.name` are unique
+- Cascade deletes on user FK; set null on `relatedUserId` (preserves transaction history)
+
+## JSON Columns (JSONB)
+- `quests.requirements`: `{ target: number }`
+- `quests.rewards`: `{ xp?: number, balance?: number }`
+- `gameSettings` fields: Typed via `.$type<T>()` — `LevelingConfig`, `EconomyConfig`, etc.
+- `guildSettings.featureOverrides`: `Record<string, boolean>` (sparse)
+- `guildSettings.colorRoleIds`: `string[]`
+- `users.settings`, `userTimers.metadata`, `items.usageData`: Untyped JSONB, default `{}`
+
+## Enums
+Defined as TypeScript enums in `shared/lib/constants.ts`, **not** as database enums. Schema columns use `varchar` with length constraints. Key enum types:
+- `TimerType`: COOLDOWN, EFFECT, ACCESS, EXAM_SYSTEM, TRIVIA_COOLDOWN
+- `TransactionType`: TRANSFER_IN, DAILY_REWARD, etc. (8 values)
+- `ModerationCaseType`: warn, timeout, kick, ban, note, prune
+- `ItemType`: MATERIAL, CONSUMABLE, EQUIPMENT, QUEST
+
+## Notable Indexes
+- `user_timers_lookup_idx`: Composite on (userId, type, key) — fast timer checks
+- `user_timers_expires_at_idx`: Expiry-based cleanup queries
+- `users_balance_idx` / `users_level_xp_idx`: Leaderboard queries
+
+## Client Setup
+- `DrizzleClient` is a singleton in `shared/db/DrizzleClient.ts` (postgres-js driver, no prefetch).
+- `withTransaction` utility in `bot/lib/db.ts` wraps Drizzle transactions and tracks count for graceful shutdown. Accepts optional existing `tx` for nested calls.
+- No soft deletes anywhere. `moderationCases` uses `active: boolean` + `resolvedAt`/`resolvedBy` for lifecycle, but rows are never deleted.