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_account.html

@@ -4,12 +4,10 @@
   <h2>Account</h2>
   <p><strong>Username:</strong> {{ request.user.username }}</p>
 
-  <h3>API Token</h3>
-  <p>Use this token as <code>Authorization: Bearer &lt;token&gt;</code> when posting artifacts.</p>
-  <p><code class="token-value">{{ token.key }}</code></p>
-  <form method="post">
-    {% csrf_token %}
-    <input type="hidden" name="action" value="regenerate">
-    <button type="submit">Regenerate Token</button>
-  </form>
+  <h3>API Keys</h3>
+  <p>
+    Posting to Daybook uses named API keys — one per agent or script, each
+    revocable on its own. You have {{ key_count }} key{{ key_count|pluralize }}.
+  </p>
+  <p><a href="{% url 'settings-api-keys' %}">Manage API keys &rarr;</a></p>
 {% endblock %}