Mobile UI pass: sheet swipe, ice-scene layering, contrast, touch targets

Phones (<=639px) only for layout/gestures; the theme-level fixes apply
everywhere, as they are token/design changes.

Settings sheet
- Swipe-to-dismiss reusing the InstallSheet gesture: the sheet follows the
  finger, closes past ~90px or on a fast flick, snaps back otherwise. Drag
  starts only from the handle/header and only while the body is scrolled to
  the top. Backdrop tap still closes.
- Fixed header + scrollable body: pb-safe + spacer, so nothing is clipped;
  a scroll cue (chevron) fades in while more content is below and out at
  the end.
- Show/Save stack under the field at 44px on phones; close, Test connection
  and Remove key are 44px too. Remove key is now a rose destructive action
  with a confirmation that the full-screen key setup comes back.
- API key note split into a short privacy line plus a collapsible
  'Using the local daemon?' tip (OLLAMA_AUTH=local / .env.local / signin).
- Fixed the missing space in the English tip ('ollama signin instead.').
- Health: kept the auto-check and banner; added a loading row and a
  'Checked just now' / 'Checked at HH:MM' freshness label (also for errors).

Ice scene / readability
- Verified the orbs were never above content (fixed z-index:-1 layer,
  pointer-events:none); they were just shining through the glass. Phones get
  lower blob/orb opacity and orbs tucked to the edges; the bottom-right orb
  is moved out from under the tab bar and the tab bar paints a more opaque
  surface so its labels hold contrast.

Contrast / themes
- Dark --text-subtle raised to #9db1d0 (8.6:1 page, 7.2:1 glass); helper
  text now uses the tokens.
- Disabled buttons are a visible muted chip (.btn-disabled) instead of a
  40%-opacity ghost.
- One ice primary gradient in both themes; danger/success now actually show
  their colour (bg-none strips the primary background-image that used to
  paint over !bg-rose-600).
- Light mode: cool card rims instead of white-on-white, stronger shadow.

Redundancy / touch
- Removed only the header gear; the hamburger drawer (folders, Settings,
  theme) and the tab-bar Settings stay.
- Theme toggle is a bordered chip with an action aria-label (drawer row too).
- Empty library hides the folder pills, demotes Import to a quiet link and
  keeps a single primary CTA. 44px targets for nav rows, segmented control
  and folder pills on phones.
- Fixed a pre-existing 16px horizontal overflow (header -mx-4 vs a
  padding-less parent) and let info values wrap instead of truncating.

Verified: mobile suite 47/47 (EN+CS, 360/390px), pixel-sampled contrast
audit 0 runs below WCAG AA (8 runs, both themes/locales; axe marks the glass
'incomplete'), i18n 27/27, desktop regression 72/72, lint + build clean.
Service worker cache bumped to freezmo-v5.

components/Sidebar.tsx

@@ -291,6 +291,7 @@ function NavContent({
         <button
           type="button"
           onClick={toggle}
+          aria-label={theme === "dark" ? t("common.switchToLight") : t("common.switchToDark")}
           title={theme === "dark" ? t("common.lightMode") : t("common.darkMode")}
           className={cn("nav-row", collapsed && "justify-center px-2")}
         >