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>

README.md

@@ -5,7 +5,7 @@ shared by the phone app, the house voice, chat, and the admin app.
 
 ## Demonstrated Skills & Tech Stack
 
-- **Core Technologies**: Go or Python service · HTTP JSON API · MQTT · LLM
+- **Core Technologies**: Go 1.25 service · HTTP JSON API · MQTT · LLM
   intent routing · OmniRoute gateway · Docker
 - **Key Tools**: Jervis (voice) · Home Assistant · Paperclip · Artemis ·
   internet use control · Apprise / NTFY · OmniRoute
@@ -82,5 +82,6 @@ flowchart LR
 The design brief is `hub_brief.md`. Project instructions are `AGENTS.md`.
 
 The interface between the Hub and every data project is `docs/ask-contract.md`.
+The frozen inbound API (ways in to the Hub) is `docs/hub-api.md`.
 Every other project is a **peer**, not a sub-project. A high-consequence control
 (for example, cutting the kids' internet) does **not** route through the Hub.