Freeze Hub inbound API v1; choose Go for the service

- docs/hub-api.md: language decision (Go 1.25) with reason and the
  frozen v1 routes POST /ask, POST /approve, GET /health, including
  request/response schemas, bearer-token auth, timeouts, error shapes,
  logging, versioning, and a safety confirmation that no route is a
  high-consequence control.
- Update README, hub_brief.md open items, and the outline docs so they
  no longer say the API is undecided or the language is open.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

hub_brief.md

@@ -221,8 +221,11 @@ Each project is a **peer**. These are talk directions, not ownership.
 ## What is still open
 
 1. **Service tokens.** One bearer token per project, stored in `environment.d`.
+   The **scheme** is frozen in `docs/hub-api.md`. Only the token values remain.
 2. **Job contract.** Exact fields for a Paperclip job (title, brief, project, agent).
 3. **Artemis voice.** Stream or file. When does phone TTS get used?
+   The **phone TTS rule** is decided in `docs/hub-api.md`, section 9.
+   The Artemis transport is still open.
 4. **Paperclip layout.** One company or several. Which projects.
 5. **Routing rules.** The first draft of `routing.md`.