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/css/pages.css

@@ -693,6 +693,38 @@
   flex-wrap: wrap;
 }
 
+/* ── Sessions ───────────────────────────────────────────────────────────────── */
+.session-row {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: .75rem;
+  padding: .6rem 0;
+  border-bottom: 1px solid var(--neu-border);
+}
+.session-row:last-child { border-bottom: none; }
+
+.session-info { display: flex; flex-direction: column; gap: .2rem; min-width: 0; }
+
+.session-browser {
+  display: flex;
+  align-items: center;
+  gap: .4rem;
+  font-size: .9rem;
+  color: var(--neu-text);
+  font-weight: 500;
+}
+.session-meta {
+  display: flex;
+  align-items: center;
+  gap: .3rem;
+  font-size: .75rem;
+  color: var(--neu-text-muted);
+  flex-wrap: wrap;
+}
+.session-sep { opacity: .4; }
+.session-id { font-family: monospace; opacity: .6; }
+
 /* ── Logo auth LineIcons ─────────────────────────────────────────────────────── */
 .logo-icon {
   font-size: 2.5rem;