Add support tickets that work with private threads

Members open a ticket from a panel in the ticket channel: one button per
category (a dropdown past five), then a short form. Each ticket is a private
thread named after the category, number and opener, with a first message
that mentions the category's staff role so its members join, and Claim and
Close buttons.

- Claim: staff (the category's role, or Manage Threads / Manage Server)
  take a ticket; the first message shows who has it.
- Close: the opener or staff close it, with an optional reason. The thread
  is locked and archived, and the log channel gets a summary and a .txt
  transcript of the whole thread.
- /ticket add|remove|claim|close inside a ticket; /tickets setup,
  /tickets category add|remove|list and /tickets panel for admins.
- Per-member limit on open tickets (default 1), per-server ticket numbers
  handed out atomically, a deleted thread closes its ticket.
- The dashboard asks the bot to post or refresh the panel through
  ticket_commands (LISTEN/NOTIFY, like music); the listener reconnects if
  the database connection drops.
- Setup warns about missing bot permissions in the ticket and log channels.

The flows live in internal/tickets behind small Discord and store
interfaces, with unit tests on fakes; the repo and the listener have
integration tests (-tags integration, TICKETS_TEST_DB).

Needs the ticket tables (velox-dashboard-api migration 000016_tickets).
.gitignore gains the /tldr benchmark rules so private chat exports and
benchmark results on disk can't be committed from this branch.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/commands/help/help.go

@@ -84,6 +84,15 @@ func HelpHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
 					"`/projects create name:\"...\" [description]` — Create a project (**Manage Server**)\n" +
 					"`/projects add-helper project-id:<id> user:@someone` — Add helper (**Manage Server**)",
 			},
+			{
+				Name: "Tickets",
+				Value: "" +
+					"Open a ticket from the panel: you get a private thread with the staff.\n" +
+					"`/ticket add user:@someone` — Add someone to your ticket\n" +
+					"`/ticket close [reason]` — Close the ticket (opener or staff)\n" +
+					"`/ticket claim`, `/ticket remove user:@someone` — Staff only\n" +
+					"`/tickets setup`, `/tickets category add|remove|list`, `/tickets panel` — Set up (**Manage Server**)",
+			},
 			{
 				Name: "Meetings (**Manage Server**)",
 				Value: "" +