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)

install.sh

@@ -398,6 +398,11 @@ fi
 echo ""
 info "✅ Skald Circle ${VERSION} installed successfully!"
 echo ""
+
+# Write channel tag and version for future updates
+echo "release" > "$INSTALL_DIR/.release-channel"
+echo "$VERSION" > "$INSTALL_DIR/.release-version"
+
 echo "  Server : ${INSTALL_DIR}/run.sh"
 echo "  Binary : ${INSTALL_DIR}/bin/skald"
 echo "  Setup  : ${INSTALL_DIR}/bin/skald-setup"