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/manifest.json

@@ -0,0 +1,17 @@
+{
+  "name": "ProxmoxPanel",
+  "short_name": "PxPanel",
+  "description": "Interface de gestion Proxmox",
+  "start_url": "/dashboard.html",
+  "display": "standalone",
+  "background_color": "#1a1a2e",
+  "theme_color": "#6c8ef4",
+  "icons": [
+    {
+      "src": "/icons/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}