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/tickets/transcript.go

@@ -0,0 +1,88 @@
+package tickets
+
+import (
+	"fmt"
+	"strings"
+
+	"velox-bot/internal/db/repos/ticketrepo"
+
+	"github.com/bwmarrin/discordgo"
+)
+
+// maxTranscriptMessages bounds how far back a transcript reads: 50 pages of
+// 100, far beyond any normal ticket.
+const maxTranscriptMessages = 5000
+
+// Transcript renders the whole thread as plain text, oldest first, and
+// reports how many messages it holds. Attachments and embeds are listed so
+// the log keeps their links and titles.
+func Transcript(d Discord, t *ticketrepo.Ticket) ([]byte, int, error) {
+	var msgs []*discordgo.Message
+	before := ""
+	var fetchErr error
+	for len(msgs) < maxTranscriptMessages {
+		page, err := d.ChannelMessages(id(t.ThreadID), 100, before, "", "")
+		if err != nil {
+			fetchErr = err
+			break
+		}
+		msgs = append(msgs, page...)
+		if len(page) < 100 {
+			break
+		}
+		before = page[len(page)-1].ID
+	}
+
+	var b strings.Builder
+	fmt.Fprintf(&b, "Ticket #%04d · %s\n", t.Number, t.CategoryName)
+	fmt.Fprintf(&b, "Subject: %s\n", t.Subject)
+	fmt.Fprintf(&b, "Opened by user %d on %s\n", t.OpenerID, t.CreatedAt.UTC().Format("2006-01-02 15:04 MST"))
+	if fetchErr != nil {
+		fmt.Fprintf(&b, "Note: only part of the thread could be read (%v)\n", fetchErr)
+	}
+	b.WriteString(strings.Repeat("-", 60) + "\n\n")
+
+	// Discord returns newest first.
+	for i := len(msgs) - 1; i >= 0; i-- {
+		writeMessage(&b, msgs[i])
+	}
+	return []byte(b.String()), len(msgs), fetchErr
+}
+
+func writeMessage(b *strings.Builder, m *discordgo.Message) {
+	name := "unknown"
+	if m.Author != nil {
+		name = m.Author.Username
+		if m.Author.GlobalName != "" {
+			name = m.Author.GlobalName + " (" + m.Author.Username + ")"
+		}
+		if m.Author.Bot {
+			name += " [bot]"
+		}
+	}
+	fmt.Fprintf(b, "[%s] %s\n", m.Timestamp.UTC().Format("2006-01-02 15:04"), name)
+
+	if content := strings.TrimSpace(m.Content); content != "" {
+		for _, line := range strings.Split(content, "\n") {
+			b.WriteString("    " + line + "\n")
+		}
+	}
+	for _, e := range m.Embeds {
+		if e == nil {
+			continue
+		}
+		title := e.Title
+		if title == "" {
+			title = clip(e.Description, 120)
+		}
+		if title != "" {
+			b.WriteString("    [embed] " + strings.ReplaceAll(title, "\n", " ") + "\n")
+		}
+	}
+	for _, a := range m.Attachments {
+		if a != nil {
+			b.WriteString("    [file] " + a.Filename + " " + a.URL + "\n")
+		}
+	}
+	b.WriteString("\n")
+}