Match the deck-creation CTA to the homework CTA layout

- "Freeze my deck" is now a full-width (w-full) button in its sticky bar,
  like "Make my homework", instead of a compact left-aligned button in a
  flex row.
- The status/validation line ("Add a photo or a document (or some text) to
  start.") moved from above the button to centred directly underneath it,
  with the same 12px muted styling the homework flow uses.
- Both flows now share the Button size="lg" shape (44px tall, 14px radius,
  same muted disabled chip, centred text); hover/disabled behaviour comes
  from the same .btn-primary/.btn-disabled classes.

Service worker: freezmo-v12.

Verified: CTA-parity suite 32/32 (full-width ratio ~1.0 at 390px and 1280px,
44px height, centred helper under the button on both pages, identical radius
and disabled chip, enabled ice gradient), mobile 51/51, i18n 27/27, desktop
regression 74/74. Lint + build clean.

components/UploadScreen.tsx

@@ -719,21 +719,24 @@ 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-[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)]">
+        <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. */}
+          <Button
+            size="lg"
+            className="touch-target w-full"
+            onClick={() => void generate()}
+            disabled={!canGenerate}
+          >
+            <SnowflakeIcon className="size-5" /> {t("upload.freezeDeck")}
+          </Button>
+          <p className="text-center text-[12px] text-[var(--text-subtle)]">
             {documentsBusy
               ? t("upload.readingDocs")
               : hasContent
                 ? t("upload.ready")
                 : t("upload.addToStart")}
           </p>
-            <div className="flex flex-wrap gap-2">
-              <Button size="lg" onClick={() => void generate()} disabled={!canGenerate}>
-                <SnowflakeIcon className="size-5" /> {t("upload.freezeDeck")}
-              </Button>
-            </div>
-          </div>
         </div>
       </div>
     </div>

public/sw.js

@@ -9,7 +9,7 @@
  *
  * Bumping CACHE_VERSION is how a new deploy invalidates old assets.
  */
-const CACHE_VERSION = "freezmo-v11";
+const CACHE_VERSION = "freezmo-v12";
 const SHELL_CACHE = `${CACHE_VERSION}-shell`;
 const ASSET_CACHE = `${CACHE_VERSION}-assets`;