ui: home carousel height lock + bubble polish

- Home: lock category carousel height to the tallest page so the
  Official Recommendations section below does not jump up when
  swiping to a page with fewer categories.
- CollapsibleText: raise default threshold to 25 lines and tighten
  the spacing between the expand-all button and the timestamp
  (drop the fixed h-8 and use mt-1 instead of mt-1.5).
- formatTime: always render dates as yyyy/m/d HH:mm regardless of
  locale, matching the requested timestamp format.

src/pages/Home/index.tsx

@@ -137,10 +137,15 @@ export function Home() {
   for (let index = 0; index < figmaOrderedCategories.length; index += 9) {
     categoryPages.push(figmaOrderedCategories.slice(index, index + 9));
   }
-  const activeCategoryCount = categoryPages[activeCategoryPage]?.length ?? 0;
-  const activeCategoryRows = Math.ceil(activeCategoryCount / 3);
+  // Use the tallest page so the carousel height doesn't shrink between
+  // pages — otherwise the section below jumps up when swiping to a page
+  // with fewer categories.
+  const maxCategoryRows = categoryPages.reduce(
+    (max, page) => Math.max(max, Math.ceil(page.length / 3)),
+    0,
+  );
   const mobileCategoryHeight =
-    activeCategoryRows * 88 + Math.max(0, activeCategoryRows - 1) * 8;
+    maxCategoryRows * 88 + Math.max(0, maxCategoryRows - 1) * 8;
 
   useEffect(() => {
     const row = categoryRowRef.current;