Deck chrome: neutral surfaces, borders and text (no navy leftovers)

- The study feed's progress header and bottom pager no longer use the old
  navy glass: new .study-chrome class uses the neutral surface token
  (same gray as the cards, #2f2f2f in dark), the neutral border
  (8% white in dark, #e5e5e5 in light) and a neutral shadow.
- Close tile, streak pill and XP pill now use --surface-sunken /
  --text-muted, matching the app's other buttons and chips; the close
  glyph is the shared XIcon.
- Bottom pager: counter in --text, arrows in --text-muted.
- .glass (mobile header) no longer has the hardcoded #101720 navy; it is
  now color-mix of the surface token. Removed the unused --color-night-*
  tokens and the last night- usage (create screen sticky bar).
- Hidden the 'Swipe up' hint on desktop, where it collided with the
  bottom pager.

New deck-chrome suite: 15/15 (computed surfaces/borders/text in both
themes, no navy); pwa 16/16, final-ux 12/12, security 8/8, contrast 20/20.

components/UploadScreen.tsx

@@ -719,7 +719,7 @@ export function UploadScreen() {
           </div>
         </section>
 
-        <div className="sticky bottom-[calc(env(safe-area-inset-bottom,0px)+4.6rem)] z-20 -mx-4 border-t border-[var(--hairline)] bg-white/65 px-4 py-3 backdrop-blur-2xl dark:bg-night-950/70 sm:bottom-0 sm:mx-0 sm:rounded-[1.35rem] sm:border sm:px-5">
+        <div className="sticky bottom-[calc(env(safe-area-inset-bottom,0px)+4.6rem)] z-20 -mx-4 border-t border-[var(--hairline)] bg-white/65 px-4 py-3 backdrop-blur-2xl dark:bg-[color-mix(in_oklab,var(--surface)_70%,transparent)] sm:bottom-0 sm:mx-0 sm:rounded-[1.35rem] sm:border sm:px-5">
           <div className="flex flex-wrap items-center justify-between gap-3">
             <p className="text-[12.5px] text-[var(--text-subtle)]">
               {documentsBusy