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/00-index.md

@@ -14,6 +14,7 @@ Read this index to inject the exact file you need. Do not search all files.
 | **Code Structure Map** | `docs/outline/03-code-map.md` | Shows the planned folder layout and entry points. |
 | **AI Agent Runbook** | `docs/outline/04-agent-runbook.md` | Gives steps to build, test, and restart Hub work. |
 | **Ask Contract** | `docs/ask-contract.md` | The interface between the Hub and every data project. |
+| **Hub Inbound API** | `docs/hub-api.md` | The frozen v1 API from every way in to the Hub. |
 | **Design Brief** | `hub_brief.md` | The agreed design. This file is the source of truth. |
 | **Project Rules** | `AGENTS.md` | Mission, rules, build order, and project relations. |
 
@@ -29,7 +30,7 @@ hold a personality or a memory. The Hub does not do the destination work.
 
 - **Env File**: `~/.config/environment.d/10-secrets.conf`
 - **Config Directory**: `docs/`
-- **Active Ports**: Hub port not allocated yet.
+- **Active Ports**: Hub 8787 (`HUB_PORT`, proposed default — confirm before deploy).
 
 ## Agent Restart Steps