feat: sessions management, web manifest, square icon-only buttons, remove lang select

- Backend: migration 002 adds user_agent/ip/last_used_at to refresh_tokens
- Backend: GET /api/auth/sessions + DELETE /api/auth/sessions/{id} endpoints
- Frontend: profile page — sessions section (browser, IP, datetime, revoke)
- Frontend: web manifest + SVG icon for PWA support
- Frontend: remove language selector from all navbars (moved to profile page)
- Frontend: neu-btn--icon-sm class for square icon-only buttons (theme/logout/edit)
- Frontend: manifest link added to all 9 HTML pages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/updates.html

@@ -10,6 +10,7 @@
   <link rel="stylesheet" href="/css/light.css" />
   <link rel="stylesheet" href="/css/pages.css" />
   <link rel="stylesheet" href="/css/lineicons-duotone.css" />
+  <link rel="manifest" href="/manifest.json" />
   <script src="/js/vendors/htmx.min.js"></script>
   <script src="/js/vendors/swup.iife.js"></script>
   <script src="/js/app.js"></script>
@@ -42,13 +43,10 @@
   <nav class="navbar" x-data="navbar()" x-cloak>
     <h2 class="navbar-title" x-text="t('nav.updates')"></h2>
     <div class="navbar-actions">
-      <select class="neu-input neu-input--sm" x-model="lang" @change="setLang($event.target.value)">
-        <option value="fr">FR</option><option value="en">EN</option>
-      </select>
-      <button class="neu-btn neu-btn--sm" @click="toggleTheme()" :title="theme==='dark'?t('navbar.lightMode'):t('navbar.darkMode')">
+      <button class="neu-btn neu-btn--sm neu-btn--icon-sm" @click="toggleTheme()" :title="theme==='dark'?t('navbar.lightMode'):t('navbar.darkMode')">
         <i :class="theme==='dark' ? 'lnid-sun-1' : 'lnid-moon-half-left-1'"></i>
       </button>
-      <button class="neu-btn neu-btn--sm" @click="logout()" :title="t('navbar.logout')">
+      <button class="neu-btn neu-btn--sm neu-btn--icon-sm" @click="logout()" :title="t('navbar.logout')">
         <i class="lnid-power-button"></i>
       </button>
     </div>