Add /closing-time, posted automatically when the space closes

[NinjaLikesCheez]

Members can post a closing-time reminder with /closing-time. The same send path runs automatically after a confirmed space-closed announcement. Admins set the text with /admin closing-time set.

Behaviour

• One feature (features/closing-time), one send path: both the slash command and the space-closed hook announce closing.time through the Announcer. The Discord adapter publishes it; the feature never talks to Discord.
• /closing-time access.minTier: member. Posts to a configured channel (typically members). No new capability.
• /admin closing-time set access.minTier: admin. Opens a modal; if a message is already saved, the modal is prefilled so it can be tweaked. The submitted text is written atomically to PIXEL_DATA_DIR/closing-time.md. On Azure that directory is the Files share (/app/persist/data) — the write persists there; there is no extra sync step.
• Mentions stay disabled on the Discord post.
• If posting is off: /closing-time replies privately that it is off; the auto path logs closing_time.disabled and does not fail space-close. Admins can still set the text.
• just register must be re-run after this rename so Discord lists /admin closing-time set instead of /admin set closing-time.

Configure

What	How
Where / whether	DISCORD_CLOSING_TIME_CHANNEL_ID — a Discord channel ID, or unset / off / none to disable both post paths
Content	/admin closing-time set (modal, prefilled when a message is already saved), or edit data/closing-time.md / PIXEL_CLOSING_TIME_FILE. Missing or empty → built-in English default. Pixel reads the file each time it posts.

The body is a file, not an env var, because it is typically a multi-line checklist (awkward in .env and Azure settings) and is not a secret. Do not put door codes or passwords in it. Operator text in the portable text field goes through escapeMarkdown; Discord posts the body as written with mentions off (same idea as /schedule).

Auth

No new capability. Does not touch core/access*, core/identity*, core/registry* or services/access-config*.

Needs a human reviewer: core/command.ts and core/dispatcher.ts — beforeForm may now return values so a form can open with saved text. Access checks are unchanged.

Live try on pixel-dev

After the first deploy, /closing-time showed Discord's "I don't know that command" / an interaction error and then still posted. That was two Pixels on the Pixel Dev token: Azure pixel-dev--0000008 plus a leftover local pixel-main container (schedule-posts worktree, same app/guild). The leftover instance is stopped. Azure is one healthy replica. Discord 40060/10062 is now logged as discord.duplicate_handler instead of reported as a crash.

Retry /closing-time and /admin closing-time set on Pixel Dev after this revision is deployed and registered. Do not also run just dev or another container on that token.

Tests

just check passed (1649 tests). Fake CommandContext and fake announcer. Dispatcher tests for guest/member deny, admin write, and modal prefill.

Off origin/main. Not mixed with Tailscale / #76.