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>

docs/outline/03-code-map.md

@@ -16,9 +16,11 @@ central_ai_llm_master/
     diagrams/               rendered images
     archify/                Archify JSON input
     outline/                AI context documents
+    ask-contract.md         Hub to project interface
+    hub-api.md              frozen inbound API (v1)
     vikunja-tasks.json      human task list
   src/                      Hub service code (to build)
-    main.*                  HTTP entry point
+    main.go                 HTTP entry point
     hear/                   takes voice or text
     understand/             LLM intent routing
     check/                  authorization and approval
@@ -36,11 +38,11 @@ central_ai_llm_master/
 | `POST /approve` | Admin app confirms a restricted action. |
 | `GET /health` | Liveness check. |
 
-The API contract is not final. See `hub_brief.md`.
+The inbound API is frozen. See `docs/hub-api.md`.
 
 ## Primary Dependencies
 
-- HTTP server (Go or Python — decide before build).
+- HTTP server (Go 1.25, standard library `net/http`).
 - HTTP client for OmniRoute, Home Assistant, Paperclip.
 - MQTT client for voice topics.
 - Tavily API client for web search.