[Refactor] Remove customizable Vibes settings

[roomote-roomote]

Opened on behalf of Bruno Bergher. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

Removes the Vibes admin settings page and all deployment-level customization behind it:

• Deletes the Vibes UI, navigation entry, tRPC API, and public docs page
• Drops style_guidance, slack_summon_emoji, slack_ack_emoji, and slack_completion_emoji from deployment_settings (migration 0012_motionless_mauler)
• Keeps fixed Slack lifecycle reactions (eyes, white_check_mark, x, and thumbsdown/-1 for closed PRs) as non-customizable defaults
• Keeps the default Roomote tone/style guidance as a discrete file, with no organization override path
• Removes emoji-reaction agent summoning entirely

Why this change was made

Vibes mixed optional branding knobs (custom reactions, summon emoji, tone overrides) into product settings and scattered them through Slack launch and agent prompt paths. The product direction is to keep a small fixed set of reactions and the built-in tone, without per-deployment customization or emoji-as-task-entry.

Impact

• Admins no longer see or configure Vibes settings
• Existing customized values are dropped (no legacy migration for user data)
• Slack tasks still use fixed ack/completion/cancel reactions; reaction-based summon no longer starts tasks
• Style overrides no longer layer onto the default Roomote tone

Screenshots

[roomote-roomote]

1 issue outstanding. See task

• apps/worker/src/callbacks/slack-mention.ts:649-650 Preserve the payload's acknowledgement emoji when cleaning up in-flight runs created before this deploy. Those runs can already have a custom reaction applied and persisted; always removing eyes leaves the actual reaction behind and triggers the retry/warn path, while falling back to the default only when the payload omits ackEmoji keeps all new runs fixed to eyes.

_{Reviewed feb47e3}