Add update.sh, release-channel tagging, mobile settings page

install.sh / install-nightly.sh:
  - Write .release-channel file ('release' or 'nightly') for future updates
  - install.sh also writes .release-version (for update --check)

update.sh (new):
  - Reads .release-channel to determine which channel to pull from
  - Release: checks releases/LATEST vs .release-version, skips if current
  - Nightly: always downloads latest
  - Stops service before extraction, restarts after
  - Rebuilds Python venv on update

ci/package.sh:
  - Include update.sh in distribution tarball

Web / mobile:
  - Add settings-page component for mobile
  - Wire settings page into mobile-app navigation
  - Chat page: load current user (/api/auth/me) for sender identity
  - Full mobile.css redesign
  - i18n: add mobile settings strings (en/fr/it)

web/i18n/en.js

@@ -58,6 +58,10 @@ export default {
   'mobile.nav.chat':     'Chat',
   'mobile.nav.alerts':   'Alerts',
   'mobile.nav.settings': 'Settings',
+  'mobile.settings.theme':    'Theme',
+  'mobile.settings.light':    'Light',
+  'mobile.settings.dark':     'Dark',
+  'mobile.settings.language': 'Language',
   'chat.send':          'Send',
   'chat.stop':          'Stop',
   'chat.thinking':      'Thinking…',

web/i18n/fr.js

@@ -58,6 +58,10 @@ export default {
   'mobile.nav.chat':     'Discussion',
   'mobile.nav.alerts':   'Alertes',
   'mobile.nav.settings': 'Paramètres',
+  'mobile.settings.theme':    'Thème',
+  'mobile.settings.light':    'Clair',
+  'mobile.settings.dark':     'Sombre',
+  'mobile.settings.language': 'Langue',
   'chat.send':          'Envoyer',
   'chat.stop':          'Arrêter',
   'chat.thinking':      'Réflexion…',

web/i18n/it.js

@@ -58,6 +58,10 @@ export default {
   'mobile.nav.chat':     'Chat',
   'mobile.nav.alerts':   'Avvisi',
   'mobile.nav.settings': 'Impostazioni',
+  'mobile.settings.theme':    'Tema',
+  'mobile.settings.light':    'Chiaro',
+  'mobile.settings.dark':     'Scuro',
+  'mobile.settings.language': 'Lingua',
   'chat.send':          'Invia',
   'chat.stop':          'Ferma',
   'chat.thinking':      'Sto pensando…',