P4-C: PWA installable, service worker push & campagne de fiabilité dialogues

- PWA: public/manifest.webmanifest + icon.svg + meta index.html (theme-color, apple-touch-icon)
- public/sw.js: service worker push-only (push → showNotification tag=sessionId ;
  notificationclick → focus/ouvre /sessions/<id>) — pas de précache (hors périmètre)
- lib/push.ts + stores/push.ts: enable/disable, abonnement VAPID, enregistrement SW au boot
- DashboardView: toggle « Notifications » (gardé par pushSupported) + i18n en/fr
- campagne de fiabilité (verdict S3): classification de tous les types de dialogue sur captures
  réelles (trust/permission×2/question) + refus Esc (deny-esc2) + plan (synthétique)
- acceptance-p4.mjs: VAPID/auth/Origin, subscribe idempotent/unsubscribe, answer (rejets)

Choix: SW écrit à la main plutôt que vite-plugin-pwa (qui tirait ~295 paquets Workbox +
2 vulns esbuild high pour un SW push-only). Zéro dépendance front nouvelle. 175 tests verts,
acceptance p1..p4 ALL GREEN.

packages/web/src/views/DashboardView.vue

@@ -7,10 +7,21 @@
         <div class="ml-auto flex items-center gap-2">
           <RouterLink :to="{ name: 'sessions' }" class="btn">{{ t('dashboard.allSessions') }}</RouterLink>
           <button class="btn" :disabled="store.loading" @click="store.fetchAll()">{{ t('sessions.refresh') }}</button>
+          <button
+            v-if="push.supported"
+            class="btn"
+            :class="push.enabled ? 'border-emerald-700 text-emerald-300' : ''"
+            :disabled="push.busy"
+            :title="pushErrorText"
+            @click="push.toggle()"
+          >
+            {{ push.enabled ? t('push.disable') : t('push.enable') }}
+          </button>
           <LanguageSwitcher />
           <button class="btn" @click="onLogout">{{ t('common.logout') }}</button>
         </div>
       </header>
+      <p v-if="pushErrorText" class="text-xs text-amber-400">{{ pushErrorText }}</p>
 
       <form class="flex flex-col gap-2 rounded-lg border border-zinc-800 bg-zinc-900/50 p-3 sm:flex-row sm:items-end" @submit.prevent="onAddRepo">
         <label class="flex flex-1 flex-col gap-1 text-xs text-zinc-400">
@@ -33,12 +44,13 @@
 </template>
 
 <script setup lang="ts">
-import { onMounted, ref } from 'vue';
+import { computed, onMounted, ref } from 'vue';
 import { useRouter } from 'vue-router';
 import { useI18n } from 'vue-i18n';
 import { useAuthStore } from '../stores/auth';
 import { useWorktreesStore } from '../stores/worktrees';
 import { useSessionsStore } from '../stores/sessions';
+import { usePushStore } from '../stores/push';
 import LanguageSwitcher from '../components/LanguageSwitcher.vue';
 import RepoSection from '../components/RepoSection.vue';
 
@@ -47,11 +59,19 @@ const router = useRouter();
 const auth = useAuthStore();
 const store = useWorktreesStore();
 const sessions = useSessionsStore();
+const push = usePushStore();
 
 const newPath = ref('');
 const adding = ref(false);
 const addError = ref<string | null>(null);
 
+// 'denied'/'unsupported' sont des clés i18n ; tout autre message d'erreur est affiché tel quel.
+const pushErrorText = computed(() => {
+  const e = push.error;
+  if (!e) return '';
+  return e === 'denied' || e === 'unsupported' ? t(`push.${e}`) : e;
+});
+
 onMounted(() => {
   void store.fetchAll();
   store.startRealtime();
@@ -59,6 +79,7 @@ onMounted(() => {
   // suit leurs mises à jour temps réel pour que les badges d'état (busy/waiting/idle) restent live.
   void sessions.fetchSessions();
   sessions.startRealtime();
+  void push.refresh();
 });
 
 async function onAddRepo(): Promise<void> {