Add Slack context source

[luca-martial]

Scope

Build a slack context-source adapter that ingests messages from allowlisted Slack channels — not every message — and writes them as Markdown.

Where to start

• Adapter directory: packages/context/src/ingest/adapters/slack/
• Model on packages/context/src/ingest/adapters/notion/
• Use the Slack Web API: conversations.pins.list and Canvas endpoints
• Auth via Slack bot token (xoxb-) with scopes channels:history, groups:history, pins:read, canvases:read
• Configuration requires a channel allowlist — never ingest a workspace's full history
• Wire the new driver value in packages/context/src/project/driver-schemas.ts
• Add docs in docs-site/content/docs/integrations/context-sources.mdx

Acceptance criteria

• New adapter under adapters/slack/ with tests
• Reads pinned messages and canvases from configured channels only
• Output writes Markdown under wiki/global/
• Authentication uses Slack bot token via env: reference
• Errors clearly if the allowlist is empty (no accidental full-workspace dumps)
• Integration docs added with the required Slack app scopes

Reward

Merging this PR earns the t-shirt tier (tier-2). See CONTRIBUTING.md.

Comment on this issue to claim it before starting work.

[mysubb01]

I'd like to claim this and work on the Slack context-source adapter. I'll keep the PR focused on the allowlisted pinned-message/canvas ingestion path, tests, driver schema wiring, and docs.

[luca-martial]

I'd like to claim this and work on the Slack context-source adapter. I'll keep the PR focused on the allowlisted pinned-message/canvas ingestion path, tests, driver schema wiring, and docs.

Thanks for being willing to take this one. I just changed the description to include all allow listed channels, not just pinned ones. You can also ignore canvases.