v0.27.0:0 - in-app settings gear + swap-lock route fix

Move the ~20 optional cluster knobs out of the StartOS "Configure Sparks"
action (now just the 4 required fields) and into a dashboard ⚙ Settings gear,
backed by a /data/app_settings.json overlay keyed by env-var names. One shared
mutable Settings instance + Settings.reload() applies edits live without a
restart; existing installs' values migrate automatically on first boot.

Also: support-service ports (parakeet/kokoro/embed/qdrant + vllm) are now
configurable, and GET /api/swap/lock no longer 404s (it was shadowed by the
/api/swap/{job_id} catch-all). WebhookNotifier is re-pointed on save so its
url/secret reload live too.

image/app/static/index.html

@@ -17,14 +17,28 @@
       <span class="muted">connecting…</span>
     </div>
     <a id="open-webui-link" class="topbar-btn hidden" href="#" target="_blank" rel="noopener" title="Open Open WebUI">Open chat ↗</a>
+    <button id="open-settings" class="topbar-btn" type="button" title="Settings" aria-label="Open cluster settings">⚙ Settings</button>
   </header>
 
   <main>
     <section id="setup-banner" class="banner hidden">
       <strong>Configuration needed.</strong>
-      <span>Run the <em>Configure Sparks</em> action in StartOS to set hostnames, then run <em>Test Connection</em>.</span>
+      <span>Run the <em>Configure Sparks</em> action in StartOS to set your two Spark IPs and SSH users. Everything else (ports, services, integrations) lives under <em>⚙ Settings</em> above.</span>
     </section>
 
+    <dialog id="settings-dialog" class="modal">
+      <form method="dialog" class="modal-form" id="settings-form">
+        <h3>Settings</h3>
+        <p class="muted small">Optional cluster knobs — vLLM/​service ports, container names, support-service hosts, and integrations. The two Spark IPs and SSH users are set once via the <em>Configure Sparks</em> action in StartOS; everything else is here. Changes apply immediately. Stored on this server and included in StartOS backups.</p>
+        <div id="settings-body" class="settings-body"><p class="muted small">Loading…</p></div>
+        <p id="settings-error" class="muted small dd-error hidden"></p>
+        <div class="modal-actions">
+          <button type="button" id="settings-cancel" class="btn">Cancel</button>
+          <button type="submit" id="settings-save" class="btn primary">Save</button>
+        </div>
+      </form>
+    </dialog>
+
     <section id="hardware-panel" class="hardware-panel hidden">
       <div class="section-header">
         <h2 class="section-title">Spark hardware</h2>