[Feat] Announce primary-branch pushes across source-control providers

[roomote-roomote]

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

What changed

• Add Merge announcer as a configurable built-in automation for GitHub, GitLab, Azure DevOps, Bitbucket, and Gitea.
• Normalize provider push payloads into one shared commit event, filter against each active repository's stored default branch, summarize commits with the deployment helper model, and include pusher and author attribution.
• Reuse provider-scoped webhook delivery IDs to suppress duplicate announcements and report delivery failures in webhook run state.
• Deliver through the standard automation destination picker: choose Slack, Teams, Telegram, or Discord, then a channel or DM me; choose Default for the Manager Channel or primary-conversation fallback.
• Persist destinations only as canonical AutomationTarget channel/user kinds. Existing saved targets populate the standard picker, while the unshipped Merge-announcer-specific Slack/Discord request fields and fallback save path are removed.
• Scope Merge announcer destination and frequency writes to its own settings save so unrelated or stale form submissions cannot overwrite a newer destination.
• Update settings, run status, telemetry, documentation, provider subscriptions, and focused provider, deduplication, destination, persistence, UI, and CI coverage.

Why this change was made

Teams need a concise notification when commits land on primary branches, including direct pushes that do not arrive through a merged pull request. Reusing Roomote's existing webhook, helper-model, canonical destination, and communication abstractions keeps behavior consistent across providers without creating a second event or notification system.

Impact

Admins can enable Merge announcer and use the same provider plus Channel/DM destination control as custom automations. Once enabled, primary-branch pushes produce one attributed summary per provider delivery; feature branches, branch deletions, inactive repositories, and duplicate deliveries remain silent. Existing canonical channel or user targets remain readable, and unrelated automation saves preserve the current Merge announcer configuration.

Screenshots

[roomote-community]

No code issues found. See task

• Unrelated automation saves can overwrite a Merge announcer destination from a stale form snapshot. (apps/web/src/trpc/commands/automations/settings-update.ts:929)

_{Reviewed ff7f574}

[roomote-roomote]

Resolved the Test check failures, replaced Merge announcer's provisional Slack/Discord controls with the shared provider plus Channel/DM picker, removed the unshipped legacy request fields, and fixed the unrelated-save race from the latest review. The final reviewed head is ff7f574; the PR description now contains current behavior and fresh visual proof.