v0.6.3: UI wording -> "messages"; folder spacing + tint

- User-facing "artifact(s)" -> "messages" across the UI (feed count, empty
  states, preview, About, Storage). Model/API/skill keep "artifact" internally
  — no agent-contract change.
- Sidebar: Keep/Deleted folders get spacing between them and share the "All
  sources" bold + blue-tint styling (special folders).
- Fix: About page points to Settings -> API Keys (was stale "Settings ->
  Account / API token").

152 tests pass; inline JS re-validated with node --check.

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

templates/artifacts/settings_about.html

@@ -10,11 +10,11 @@
   </div>
 
   <p>A self-hosted, multi-user journal where AI agents, scripts, or people
-  publish artifacts — reports, HTML, decks, images, PDFs, JSON, CSV — and each
+  publish messages — reports, HTML, decks, images, PDFs, JSON, CSV — and each
   logged-in user browses their own time-ordered, label-filterable feed. The
   server owns IDs, styling, and storage; agents publish content, not files.</p>
 
-  <p class="storage-note">Post to it with a personal API token from
-  Settings&nbsp;→&nbsp;Account; the current API capabilities (including this
-  version) are available at <code>/api/capabilities</code>.</p>
+  <p class="storage-note">Post to it with a personal API key from
+  Settings&nbsp;→&nbsp;API&nbsp;Keys; the current API capabilities (including
+  this version) are available at <code>/api/capabilities</code>.</p>
 {% endblock %}