Make the Freeze my deck button text-only, matching Make my homework

The two CTAs already shared the same Button size="lg" shape (full-width,
44px, 14px radius, muted disabled chip, helper line centred underneath);
the last visible difference was the snowflake icon on "Freeze my deck".
Dropped it so the button is text-only exactly like "Make my homework" —
the snowflake stays on the hero, the drop zone and the tab bar.

Service worker: freezmo-v13.

Verified: computed-style diff between the two buttons is now empty (same
classes and every measured property), CTA-parity suite 32/32, desktop
regression 74/74, mobile 51/51, i18n 27/27. Lint + build clean.

components/UploadScreen.tsx

@@ -720,15 +720,15 @@ export function UploadScreen() {
         </section>
 
         <div className="sticky bottom-[calc(env(safe-area-inset-bottom,0px)+4.6rem)] z-20 -mx-4 space-y-2 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">
-          {/* Same CTA shape as the homework flow: a full-width button with the
-              helper line centred underneath. */}
+          {/* Same CTA shape as the homework flow: text-only, full-width, with
+              the helper line centred underneath. */}
           <Button
             size="lg"
             className="touch-target w-full"
             onClick={() => void generate()}
             disabled={!canGenerate}
           >
-            <SnowflakeIcon className="size-5" /> {t("upload.freezeDeck")}
+            {t("upload.freezeDeck")}
           </Button>
           <p className="text-center text-[12px] text-[var(--text-subtle)]">
             {documentsBusy