Redesign watch history cards and fix timestamp display bug

- Redesigned watch history cards to use a list view layout (flex-row) for better space utilization on both desktop and mobile.
- Updated `buildHistoryCard` in `js/historyView.js` to support a `variant` prop ('compact' or 'modal') for context-specific sizing.
- Updated `js/ui/profileModalController.js` to pass `variant: "modal"` to the watch history renderer.
- Fixed a bug where the "Watched [time] ago" timestamp was unavailable because `normalizeHistoryItems` failed to check `pointer.watchedAt`.
- Verified changes with a reproduction script for the timestamp bug and existing unit tests for the controller.

js/ui/profileModalController.js

@@ -1892,6 +1892,7 @@ export class ProfileModalController {
       featureBannerSelector: "#profileHistoryFeatureBanner",
       sessionWarningSelector: "#profileHistorySessionWarning",
       emptyCopy: "You haven’t watched any videos yet.",
+      variant: "modal",
       remove: (payload) =>
         this.callbacks.onHistoryReady({
           ...(typeof payload === "object" && payload ? payload : {}),