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/components/messageStream/CollapsibleText.tsx

@@ -28,7 +28,7 @@ export function CollapsibleText({
   children,
   className = "",
   wrapperClassName = "",
-  collapsedLines = 8,
+  collapsedLines = 25,
 }: {
   children: ReactNode;
   /** Typography classes applied to the text container. */
@@ -110,7 +110,7 @@ export function CollapsibleText({
           type="button"
           onClick={() => setExpanded((v) => !v)}
           aria-expanded={expanded}
-          className="group mt-1.5 inline-flex h-8 items-center gap-1 text-[13px] font-medium text-ark-gold transition-colors duration-200 hover:text-ark-gold2"
+          className="group mt-1 inline-flex items-center gap-1 text-[13px] font-medium leading-5 text-ark-gold transition-colors duration-200 hover:text-ark-gold2"
         >
           <span>{expanded ? t("showLess") : t("showMore")}</span>
           <m.span