External connectors relabel and the connection guides #1113

Parent: #1107 · ADR-0142 · last slice

On 2026-10-07 Vain decided that existing apps move straight to Admit automatically in the migration (the plugin has no users yet), so this slice has no opt-in step.

What to build

• Client:
  • Placing a conversation into a local Channel moves to that conversation's row in the app's conversation list ("Sync to a Channel").
  • The External connectors entry no longer offers Authorize a conversation. It keeps one advanced action, a saved-target proactive grant, as the fallback for Providers that cannot list or address conversations (Proactive posts to any conversation the platform lets the app speak in #1115). The entry is reserved for later one-way input streams such as webhooks.
  • The Lark setup guide steps shrink from account → target → identity → grant → verify to app → bind → verify.
• Docs:
  • Rewrite the Lark, Slack, Discord and WeChat connection guides (zh/en) around Bind app. Receiving, replying and proactive posts need no delivery target. Where the Bot can speak is managed by platform permissions.
  • Delivery targets move to an advanced fallback section.
  • Update the terms in CONTEXT.md/CONTEXT.zh.md (conversation entry, default traffic, new-conversation mode, app) and the Messaging section of the living architecture.
  • Add Release Ledger entries.

Acceptance criteria

• A migrated profile admits new DMs and mentions after upgrade, and conversations that were revoked before the upgrade stay blocked.
• Sync to a Channel from a conversation row works with the same authority as the old connector route.
• Saved-target proactive grants still work from the advanced section.
• Guides match the shipped UI. Screenshots are refreshed. pnpm changelog:check passes.

Blocked by

#1112.