feat: v6.0.0 PWA offline support

- manifest + icones, service worker (precache, network-first, Background Sync)

- module client FlowOffline (IndexedDB, queue, delta, flush) + hook editeur

- endpoints /api/v2/sync/{delta,batch,status} + moteur de sync (conflits LWW/orpheline/copie offline)

- migrations offline_sync_queue + sync_version (triggers)

- UI offline (banner, badge sync, toasts, icone dirty) + doc /help

- tests pytest (sync, migrations, SW, offline) + E2E Playwright; bump 6.0.0

app/templates/base.html

@@ -5,6 +5,11 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>FlowDeck — {% block title_prefix %}Home{% endblock %}</title>
   <link rel="icon" type="image/svg+xml" href="/static/favicon.svg">
+  <link rel="manifest" href="/static/manifest.json">
+  <meta name="theme-color" content="#191919">
+  <link rel="apple-touch-icon" href="/static/icons/apple-touch-icon.png">
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
   <link rel="stylesheet" href="/static/css/app.css?v=5.1.1">
   <link rel="stylesheet" href="/static/css/design-tokens.css?v=5.2.0">
   <link rel="stylesheet" href="/static/css/components.css?v=5.2.0">
@@ -750,6 +755,11 @@
     </template>
   </div>
 
+  <!-- ============ PWA SYNC BADGE (v6.0.0) ============ -->
+  <div id="fd-sync-badge" class="fd-sync-badge" style="display:none" role="status" aria-live="polite">
+    <span class="fd-sync-spinner"></span><span>Synchronisation…</span>
+  </div>
+
 </div>
 
 <script data-cfasync="false">
@@ -2271,5 +2281,55 @@
 })();
 </script>
 
+{# ─── PWA: sync indicators (v6.0.0) ─── #}
+<style>
+.fd-sync-badge{position:fixed;top:10px;right:14px;z-index:600;display:flex;align-items:center;gap:8px;
+  background:var(--bg-secondary,#262626);border:1px solid var(--border,rgba(255,255,255,.1));
+  color:var(--text-secondary,#b8b8b8);border-radius:20px;padding:5px 12px;font-size:12px;
+  box-shadow:0 4px 16px rgba(0,0,0,.35);}
+.fd-sync-spinner{width:12px;height:12px;border:2px solid rgba(255,255,255,.25);
+  border-top-color:var(--accent,#2383E2);border-radius:50%;display:inline-block;
+  animation:fd-spin .8s linear infinite;}
+@keyframes fd-spin{to{transform:rotate(360deg)}}
+.sidebar-item.fd-dirty .page-name::after{content:'⟳';margin-left:6px;font-size:11px;
+  color:var(--accent,#2383E2);opacity:.85;}
+</style>
+
+{# ─── PWA: offline client module + service worker registration (v6.0.0) ─── #}
+<script src="/static/js/offline.js?v=6.0.0" defer data-cfasync="false"></script>
+<script data-cfasync="false">
+(function() {
+  if (!('serviceWorker' in navigator)) return;
+  window.addEventListener('load', function() {
+    navigator.serviceWorker.register('/sw.js').then(function(reg) {
+      if ('sync' in reg && reg.sync) {
+        reg.sync.register('sync-flowdeck').catch(function() {});
+      }
+    }).catch(function() {});
+  });
+})();
+</script>
+
+{# ─── PWA: sync badge + toasts wiring (v6.0.0) ─── #}
+<script data-cfasync="false">
+document.addEventListener('DOMContentLoaded', function() {
+  if (!window.FlowOffline) return;
+  window.FlowOffline.onChange(function(s) {
+    var badge = document.getElementById('fd-sync-badge');
+    if (badge) badge.style.display = s.isSyncing ? 'flex' : 'none';
+  });
+  window.addEventListener('flowdeck:sync-done', function(ev) {
+    var d = ev.detail || {};
+    if (d.failed) {
+      if (window.showToast) window.showToast(d.failed + ' modification(s) non synchronisée(s)', 'error');
+    } else if (d.conflicts) {
+      if (window.showToast) window.showToast('Synchronisé — ' + d.conflicts + ' conflit(s) résolu(s)', 'info');
+    } else if (d.synced) {
+      if (window.showToast) window.showToast('Modifications synchronisées', 'success');
+    }
+  });
+});
+</script>
+
 </body>
 </html>