[verified] Security hardening + UX/UI polish

Security (requesting-code-review pipeline + independent reviewer):
- Fix path traversal on file upload (basename sanitize + resolve-containment)
- Fix IDOR: org + owner scoping on all group/chat routes (_authorize_group/_get_owned_group),
  hide other users' personal groups in listings
- Remove XSS via v-html in Chat task (text interpolation)
- Add test_security.py (traversal + cross-user denial) — all pass

UX/UI (ui-ux-pro-max + frontend-dev-verification):
- Global: focus rings, 44px touch targets, hover/press transitions, input focus glow,
  prefers-reduced-motion, skeleton loaders, empty states, back links, spinner
- Login: password toggle, autocomplete, spinner, disabled-when-empty
- Cards lift on hover; dashboard skeleton + empty state; analyze button spinner

All backend tests pass (m0/m1/routes/security/e2e); frontend builds; served SPA verified via curl.

frontend/src/views/Personas.vue

@@ -1,5 +1,6 @@
 <template>
   <div>
+    <router-link to="/" class="btn-back">← {{ i18n.t('dashboard') }}</router-link>
     <div class="row" style="align-items:center">
       <h2 style="margin:0">{{ i18n.t('personas') }}</h2>
       <span class="muted" style="margin-left:auto">Levels: choose one to practice (one-shot)</span>
@@ -8,7 +9,7 @@
     <div v-for="tier in ['A','B','C']" :key="tier" style="margin:20px 0">
       <h4>{{ tierLabel(tier) }}</h4>
       <div class="grid">
-        <div v-for="p in byTier(tier)" :key="p.id" class="card pcard">
+        <div v-for="p in byTier(tier)" :key="p.id" class="card pcard lift">
           <div class="row">
             <strong>{{ p.name }}</strong>
             <span class="badge" :class="p.my_outcome">{{ outcomeLabel(p.my_outcome) }}</span>