feat: keep Week Ahead plans through offline saves (Closes #1180)

frontend/index.html

@@ -481,6 +481,26 @@
       </div>
       <div class="small tomorrow-conflict-status" id="tomorrow-conflict-status" role="status" aria-live="assertive"></div>
     </section>
+    <section class="week-conflict-review" id="week-conflict-review" aria-labelledby="week-conflict-title" hidden>
+      <div class="small">Cross-device change</div>
+      <h3 id="week-conflict-title">Choose which Week Ahead plan to keep</h3>
+      <p class="small muted">Both complete weeks stay preserved until one choice succeeds. Today will not change.</p>
+      <div class="week-conflict-plans">
+        <section aria-labelledby="week-conflict-phone-title">
+          <h4 id="week-conflict-phone-title">This phone</h4>
+          <div id="week-conflict-phone-plan"></div>
+        </section>
+        <section aria-labelledby="week-conflict-server-title">
+          <h4 id="week-conflict-server-title">Saved on your account</h4>
+          <div id="week-conflict-server-plan"></div>
+        </section>
+      </div>
+      <div class="week-conflict-actions">
+        <button id="keep-phone-week" type="button">Keep this phone’s week</button>
+        <button id="use-server-week" type="button">Use saved account week</button>
+      </div>
+      <div class="small week-conflict-status" id="week-conflict-status" role="status" aria-live="assertive"></div>
+    </section>
     <nav class="mobile-plan-today-nav" aria-label="Plan Today sections">
       <button type="button" data-plan-today-section="fit" aria-current="location">Fit</button>
       <button type="button" data-plan-today-section="today">Today</button>