Release v0.2.0: multiple named API keys per user

Replaces the single per-user DRF token with named, individually-revocable
API keys, so you can run one key per agent and cut off a leaked one without
disrupting the others.

- New ApiKey model (user, name, dbk_-prefixed key, created_at, last_used_at).
  Data migration copies every existing authtoken 1:1 into a "default" named
  key with the same value, so no client (incl. the sibling test project's
  hardcoded test-user key) needs reconfiguring.
- Auth (resolve_token_user) resolves against ApiKey and stamps last_used_at,
  throttled to one write/minute.
- Settings -> API Keys: table with name/key/created/last-used + per-row
  revoke and a create form; keys viewable on demand. Settings -> Account now
  links here; Settings -> Users issues a named initial key.
- Gated provisioning API for test installations: GET/POST /api/keys and
  DELETE /api/keys/{id}, controlled by DAYBOOK_KEY_PROVISIONING_API (unset ->
  follows DEBUG, so off in deployment). Advertised via key_provisioning_api
  in /api/capabilities; 403 when disabled.
- Docs (api/deployment/quickstart/posting-helper), SKILL.md, and env.example
  updated from "token / Settings -> Account" to "key / Settings -> API Keys".
- Tests: new API + UI suites for keys; existing token-based tests moved to
  ApiKey. Full suite 129 passing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/agent_quickstart.md

@@ -2,10 +2,11 @@
 
 This is the shortest path for an agent to publish and retrieve artifacts from Daybook.
 
-## 0. Get Your API Token
+## 0. Get Your API Key
 
-Log in to the app in a browser and copy your personal token from **Settings → Account**
-(`http://127.0.0.1:8001/settings/account/`). Every artifact you post with it lands in your
+Log in to the app in a browser and create a personal key under **Settings → API Keys**
+(`http://127.0.0.1:8001/settings/api-keys/`). Name it after the agent so you can revoke it
+later. Every artifact you post with it lands in your
 feed, and only yours.
 
 ## 1. Check Capabilities