[chat] fix Slack streaming team ID for interactive payloads

[mdnanocom]

Fix Slack structured streaming from block_actions handlers

Calling thread.post(stream) from an onAction handler fails because recipientTeamId is derived as an object instead of a workspace ID string.

Cause

thread.handleStream used:

options.recipientTeamId = raw?.team_id ?? raw?.team;

• Message events: raw.team is "T123" → works.
• block_actions payloads: raw.team is { id: "T123", domain: "..." } → returned an object, Slack rejects the stream.

Fix

Extract the team ID with a helper that accepts every shape Slack sends:

• raw.team_id
• raw.team (string)
• raw.team.id (block_actions)
• raw.user.team_id (fallback)

Only packages/chat/src/thread.ts changes. No public API change. Only the Slack adapter reads recipientTeamId.

Tests

• Unit: parametrized over all three raw shapes + a block_actions structured‑chunk case.
• Replay: new buttonPrompt + buttonAction fixtures assert chatStream receives recipient_team_id and a task_update chunk.

[vercel]

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[mdnanocom]

@bensabic hello!
i improved the pr
do you need anything from me before merging?
thank you