[johnnyhuy]

The dashboard Documents tab now fetches the live document list and detail from the backend instead of showing a static placeholder. It adds loading, error and empty states, and leaves the Ask and Messages tabs unchanged.

Part of #5
Closes #23

Gates run locally with mise:

• mise run install - passed (backend used Python 3.13 via mise; the sandbox default Python 3.14 breaks the pinned chromadb dependency build)
• mise run test-backend - 67 passed
• mise run test-frontend - passed (repo stub, no frontend test suite yet)
• bunx tsc --noEmit in frontend - passed
• bun run build in frontend - passed, static page generated

Proof:

• API contract checked with a FastAPI TestClient fixture (mocked Slack auth, seeded SQLite). GET /api/documents returned 200 with items, total, limit and offset, most recent first. GET /api/documents/1 returned 200 with full content. Transcript saved locally at .tmp/proof/documents-api-transcript.txt and kept out of git.
• Screenshot capture was blocked in this sandbox. Listening sockets are denied, so no local server could start, and the AO browser daemon is unreachable from the sandbox. The screenshot step needs a re-run with sandbox networking enabled.
• Live backend startup was not used for proof. app.main builds the Slack Bolt app at import, which calls Slack auth.test, so starting it needs a real token. Per run safety rules no real token was touched. Fixtures and mocks only.

Known follow-ups:

• Conversations tab wiring remains for a later slice under Build conversation and document management dashboard MVP #5.
• No user-facing Slack behaviour changed.