Email ticketing fixes, comms polish, and .env cleanup

Inbound:
- Gmail poll query is:unread in:inbox (was category:primary, which matched
  nothing on a no-tabs Workspace inbox)

Outbound email:
- Closed/escalation auto-emails editable via TICKET_CLOSE_MESSAGE and new
  TICKET_ESCALATION_EMAIL_MESSAGE; drop the staff signature from closing emails
- Replies quote the customer's latest message (gmail_quote markup so clients
  collapse it), embed custom emoji inline via CID attachment, and strip Discord
  role mentions
- Tagline spacing fix in the company signature

Discord side:
- Suppress all mentions in log + transcript posts (no more pinging on close)
- Drop the staff-role ping from new-ticket and follow-up notifications
- Ticket channels inherit category permissions instead of setting per-channel
  overwrites (removes the Manage Roles requirement)

Gmail folders:
- Folder/label routing (gmailLabels.js) with /folder; close files to Complete

Config:
- Remove ~56 stale .env keys for long-removed features; refresh stale copy

Docs:
- Design specs for folder routing, email-flow toggle, and per-staff metrics

HOWITWORKS.md

@@ -3,7 +3,7 @@
 Broccolini Bot is a single Node.js process. It does three things at once:
 
 1. **Listens to Discord** — slash commands, button clicks, modals, ticket-channel messages.
-2. **Polls Gmail** — every N seconds, pulls unread `category:primary` mail and turns each thread into a Discord ticket channel.
+2. **Polls Gmail** — every N seconds, pulls unread `in:inbox` mail and turns each thread into a Discord ticket channel.
 3. **Serves a couple of HTTP endpoints** — a public healthcheck and an internal config/control API.
 
 State lives in MongoDB via Mongoose. There is no queue/worker tier and no public REST API.
@@ -27,7 +27,7 @@ Every `setInterval` in the `ready` block is wrapped through `trackInterval(...)`
 
 `gmail-poll.js`:
 
-1. Lists unread messages in `category:primary`.
+1. Lists unread messages in `in:inbox` (excludes Spam, Trash, and anything filter-skipped from the inbox).
 2. For each thread, looks up an existing `Ticket` by `gmailThreadId`. If none, creates a Discord channel under `TICKET_CATEGORY_ID` (or an overflow category if the main is full at Discord's 50-channel limit) and inserts a `Ticket` document.
 3. Posts a welcome embed + action row (Close / Claim / Escalate) into the channel and pings `ROLE_ID_TO_PING`.
 4. On subsequent emails in the same thread, just appends the new message to the existing channel.