Add /tldr: a private overview of what you missed in a channel

/tldr [since] summarizes the messages in the channel it is run in that the
caller has not been summarized yet, using a small local model on Ollama, and
replies ephemerally. The answer streams into the reply as it is written.

- Per-user, per-channel cursor (tldr_cursors) so each run picks up where the
  last left off; `since:` (e.g. 6h, 2d, max 7d) peeks without moving it.
  First use covers the last 24h, and a stale cursor never reaches back more
  than 7 days.
- Only summarizes channels both the caller and the bot can read.
- The transcript drops bots, system messages, reactions and filler, turns
  links, GIFs, images and files into short tags ([link: site], [image],
  [file: name], preview titles), marks replies, and writes a date marker
  where the chat paused for 3h or more so the model can keep topics apart.
- The prompt asks for one bullet per conversation, oldest first, with a
  worked example; it was tuned against a synthetic chat and a real export
  with qwen3:4b-instruct-2507 (the default model).
- One model call at a time across the bot, one /tldr per user.
- docker-compose: Ollama service (CPU only, 8g memory cap: 6g killed the
  runner mid-request), model pull on startup.

Needs the tldr_cursors migration (velox-dashboard-api 000016).

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

internal/commands/help/help.go

@@ -77,6 +77,12 @@ func HelpHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
 					"`/timezone set <IANA>` — Set your timezone (e.g. `Europe/Lisbon`)\n" +
 					"`/timezone show` — Show your timezone",
 			},
+			{
+				Name: "TL;DR",
+				Value: "" +
+					"`/tldr [since:<30m|6h|2d>]` — Private summary of what you missed in the channel you run it in. " +
+					"Without `since` it picks up where your last `/tldr` in that channel left off (first time: the past 24h).",
+			},
 			{
 				Name: "Projects",
 				Value: "" +