feat: name the channel, the date and the local time in the protocol

[TheMeinerLP]

Three things a reader of a meeting protocol looks for and could not find. Before and after:

+**Channel:** [Meeting-Raum](https://discord.com/channels/752…/1166…)
+**Date:** @[20.08.2026](mention://date/2026-08-20) · 15:08, 47 min · 2 participants
+
 ## Participants
 …
 ## Transcript

-**13:08:12** · @[Phillipp](mention://user/7a621c83-…) (…)
+**15:08:12** · @[Phillipp](mention://user/7a621c83-…) (…)

Times were written in UTC

The protocol is read by the people who were in the room, so the times in it are theirs. UTC was wrong in the way that is hardest to catch: 15:08 reads as a plausible meeting time whether or not it is the right one. Nothing about the document would have looked broken.

timezone is now per-guild configuration, defaulting to Europe/Berlin. An unusable value falls back to UTC with a warning naming the guild rather than failing the job — a wrong offset is recoverable, a missing protocol is not.

Checked before relying on it: the python:3.14-slim image does carry the zoneinfo database, so ZoneInfo("Europe/Berlin") resolves in the container and 13:08 UTC renders as 15:08 CEST. A slim image without tzdata would have failed only in production.

The channel was missing entirely

The worker writes the document and holds no Discord connection, so it knew only the id. The bot records the name when it opens the session — migration 0005, nullable.

Capturing it at open time rather than at render time is deliberate: a channel renamed afterwards should not rewrite the protocols of meetings held under the old name. The heading links the channel either way, falling back to the id when no name was captured, so sessions recorded before this column existed still get a working link.

The date is now an Outline date chip

@[20.08.2026](mention://date/2026-08-20) — MentionType.Date exists in the deployed version (v1.9.1), so Outline renders it as a chip rather than text.

Date only, deliberately. v1.9.1's parseMentionUrl matches [a-z0-9-]+ for the value; the datetime form (…T15:08) only arrives with the regex on main, which carries the comment "The modelId is a UUID, a date (2024-02-03) or a datetime (2024-02-03T13:00)". An ISO datetime would silently degrade to a plain link here.

The heading also carries the start time, duration and participant count.

Design note

ChannelRef is a separate value object rather than a field on Transcript: it describes the meeting, not what was said, and the name is a snapshot rather than a live lookup. render_transcript's channel parameter is optional so a caller that cannot resolve it still gets a protocol — the heading just omits that line.

Verification

369 tests pass. New tests cover: times rendered in the configured zone (22:00 Berlin, not 20:00 UTC), an unusable zone still producing a document, the channel link with and without a name, the date mention's exact form, a protocol rendering without a channel at all, and the name reaching the session row when it opens.

Checked against the defect, not just the fix: replacing the timezone lookup with a hardcoded UTC turns one of the new tests red.

One cosmetic thing I left alone: the channel name renders as Meeting\-Raum — the Markdown escaper escapes the hyphen. Outline renders it back as -, and the escaping is there because a channel name is attacker-controllable text, so I did not weaken it for looks.