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>

templates/artifacts/settings_base.html

@@ -25,6 +25,7 @@
     <nav class="settings-nav">
       <a class="settings-nav-back" href="{% url 'feed' %}">&larr; Back to Feed</a>
       <a class="{% if active_section == 'account' %}selected{% endif %}" href="{% url 'settings-account' %}">Account</a>
+      <a class="{% if active_section == 'api-keys' %}selected{% endif %}" href="{% url 'settings-api-keys' %}">API Keys</a>
       <a class="{% if active_section == 'storage' %}selected{% endif %}" href="{% url 'settings-storage' %}">Storage</a>
       <a class="{% if active_section == 'demo-data' %}selected{% endif %}" href="{% url 'settings-demo-data' %}">Demo Data</a>
       {% if request.user.is_superuser %}