v0.25.0:0 - cluster coordination layer (swap lock + webhook + schedule registry)

GPU-arbiter safety layer for when automation, not just the dashboard, swaps
models:
- swap reservation lock (POST/GET/DELETE /api/swap/lock); 423-enforced in
  post_swap via a single-read gate, TTL-bounded, secret-token auth, human
  force-release override + dashboard banner
- swap webhook (swap_complete/swap_failed) fired outside the swap lock, optional
  HMAC signature, configurable URL+secret
- read-only schedule registry (GET/POST/DELETE /api/schedule) + dashboard panel

New module image/app/coordination.py; docs/COORDINATION.md for consumers; 22
offline tests in test_coordination.py.

image/app/static/index.html

@@ -96,6 +96,13 @@
       </details>
     </section>
 
+    <section id="lock-banner" class="banner lock-banner hidden">
+      <span class="lock-icon" aria-hidden="true">🔒</span>
+      <span id="lock-text">GPU swap path reserved</span>
+      <span class="spacer"></span>
+      <button id="lock-release" class="btn small-btn">Release</button>
+    </section>
+
     <nav id="dashboard-tabs" class="dashboard-tabs hidden" role="tablist">
       <button type="button" class="dashboard-tab" data-tab="llm" role="tab" aria-selected="true">LLM</button>
       <button type="button" class="dashboard-tab" data-tab="audio" role="tab" aria-selected="false">Audio / Speech</button>
@@ -394,6 +401,14 @@
       <section id="cards" class="cards"></section>
     </section>
 
+    <section id="schedule-panel" class="schedule-panel hidden">
+      <div class="section-header">
+        <h2 class="section-title">Scheduled jobs</h2>
+      </div>
+      <p class="muted small">Registered by your own automation. Spark Control only displays these — it doesn't run them.</p>
+      <div id="schedule-list" class="schedule-list"></div>
+    </section>
+
     <section id="update-banner" class="update-banner hidden">
       <div class="ub-context muted small">
         Updates to <strong><a href="https://github.com/eugr/spark-vllm-docker" target="_blank" rel="noopener">eugr/spark-vllm-docker</a></strong>