rename path: fix env-var mismatch, gut canRename gate, add primary-bot fallback on 401/403/429

- secondary rename-bot token was set as RENAME_TOKEN in .env but utils/renamer.js reads RENAMER_BOT; silently no-op'd every rename (host .env renamed separately)
- services/tickets.js canRename gutted to an always-ok shim; Mongo 2/10min per-channel gate is redundant since renames flow through RENAMER_BOT's own bucket. Ticket.renameCount / renameWindowStart remain as orphan fields (no migration)
- handlers/buttons.js + commands.js: drop the four "Channel renamed too quickly" else-branches and the rename-countdown label suffix; replace .catch(() => {}) with .catch(err => logError('rename', err)...)
- services/channelQueue.js: executeRename falls back to channel.setName(currentName) when renamer throws err.fallback === true (401/403/429); classifies non-fallback errors as renameQueue:token/permission (401/403) or renameQueue:secondary-bot ratelimited (429)
- utils/renamer.js: on 401/403 throw err.fallback=true immediately; on 429 respect retry_after up to 2000ms then throw err.fallback=true
- docs: align CLAUDE.md, docs/api/DISCORD_API_VALIDATION.md, docs/architecture/CRITICAL_FILES_AND_HOW_IT_WORKS.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -73,7 +73,7 @@ Every `interactionCreate` branch runs through `runHandler(name, interaction, fn)
 ### Tickets (`services/tickets.js`, `models.js`)
 - `Ticket` schema has indexes on `{gmailThreadId}` (unique), `{status, lastActivity}`, `{senderEmail, status}`, `{discordThreadId}`.
 - **Discord-originated tickets** use `gmailThreadId` with prefix `discord-` / `discord-msg-` — skip the Gmail reply path entirely.
-- `canRename(ticket)` enforces Discord's 2-rename/10-min per-channel limit via **two atomic `findOneAndUpdate` calls** (reset-if-expired, then increment-if-under-limit) — never a read-then-update.
+- Renames route through `utils/renamer.js` (RENAMER_BOT secondary token). On 401/403/429 from the secondary, `services/channelQueue.js` falls back to the primary bot via `channel.setName`. `canRename()` is retained as an always-ok shim for back-compat. `Ticket.renameCount` / `Ticket.renameWindowStart` remain in the schema but are now unread/unwritten orphan fields.
 - `getOrCreateTicketCategory()` handles Discord's 50-channels-per-category ceiling by creating `"<name> (Overflow N)"` categories; `cleanupEmptyOverflowCategory()` removes empties. The primary category is never deleted.
 - Scheduled jobs in `ready`: `checkAutoClose`, `checkAutoUnclaim`, `reconcileDeletedTicketChannels`, plus `services/staffNotifications.js#notifyAllStaffUnclaimed` and the pattern/surge/chat checkers.