Remove dead/stale code, dedup close+escalation paths

Dead/stale removals (grep-confirmed no consumers):
- config: drop 9 unread CONFIG keys (ROLE_TO_PING_ID, SIGNATURE,
  REMINDER_*, RENAME_LOG_CHANNEL_ID, SETTINGS_*); remove their
  ALLOWED_CONFIG_KEYS entries and the orphaned settings-site UI fields
- configSchema: delete unreachable json/string_or_json validators
- models: drop unused ticketTag field
- gmail-poll: remove unused isPollSuspended export
- utils: remove dead htmlToTextWithBlocks/decodeHtmlEntities/BLOCK_TAG_REGEX
- internalApi: remove router._allowedKeys (test it served is gone)
- discord client: drop unused GuildPresences privileged intent
- broccolini-discord: remove dormant /api 503 gate (no /api routes)

Fixes:
- context-menu ticket create now uses makeTicketName('unclaimed', ...)
  instead of the contract-violating ticket-<n> name
- drop write-only pending.userId from both close paths

Dedup / simplify:
- new services/transcript.js shares the transcript text/date/header
  builders between the button and force-close paths (had drifted)
- resolveEscalationCategoryId() replaces 3 copies of the category logic
- ticketChannelOverwrites() shares the create-permission array between
  the two interactive ticket-create paths
- finalizeBody() shares the email-cleanup tail in parseGmailMessage
- getTicketActionRow drops its never-passed options arg;
  sendTicketNotificationEmail drops its always-null subjectLine arg
- hoist invariant guild lookup out of the auto-close/unclaim loops
- drop redundant lastActivity write (and now-dead updateTicketActivity)
- /help lists all current commands and the right-click apps

models.js

@@ -15,7 +15,6 @@ const ticketSchema = new mongoose.Schema({
     escalationTier: { type: Number, default: 0 },
     ticketNumber: Number,
     priority: { type: String, default: 'normal', enum: ['low', 'normal', 'medium', 'high'] },
-    ticketTag: String,
     lastActivity: Date,
     welcomeMessageId: String,
     claimerId: String,