Improve UX for album and space search, and add it to mobile

[LoPeraa]

Feature request

The recently added ability to search within a specific album or Space is great functionally, but the UI/UX could be improved, and it's currently missing from mobile entirely.

Suggestion

Take inspiration from YouTube's channel page pattern: right above the video grid, there are tabs (Videos/Shorts/Playlists/etc.) with a search icon on the right that scopes search to that channel specifically.

Applied here: add a search icon next to the existing "Years | Months | All" selector, consistently on both album and Space pages. This would:

• Make the scoped search more discoverable and consistent across contexts
• Enable the same interaction on mobile, where scoped search doesn't currently exist at all, by adding the search icon next to the Years/Months/All control in the bottom nav bar (mirroring how it already works on the main timeline)