feat(photos): add folder-aware browsing, search, and view modes

[veryCrunchy]

Parent epic: #14

User problem

Photos cannot currently be searched or browsed by server folder, and the user cannot choose whether a folder view includes only direct photos or also photos from nested folders. The gallery also lacks compact list and grid presentation choices. Its pill-based top-level navigation does not scale to the complete Photos experience and makes the active context harder to understand.

Goal

Provide folder-aware photo discovery, scalable adaptive navigation, and clear view controls without turning the Photos timeline into the Files browser.

Scope

• search photos and videos by folder name, path, and media metadata
• browse a folder hierarchy with useful media counts and representative thumbnails
• support explicit recursion modes:
  • folders only
  • direct photos and subfolders
  • photos from the selected folder only
  • photos from the selected folder and all subfolders
• replace the pill row with stable top-level Photos destinations such as Timeline, Folders, Albums, People, and Favorites when the server supports them
• use compact, touch-friendly navigation on phones and a persistent sidebar or rail on desktop and larger screens
• keep folder scope, recursion, sort, and grid/list controls inside the active view rather than adding more top-level destinations
• offer grid and list views with remembered per-device preferences
• preserve date sorting, RAW pairing, and future motion/live-photo grouping in every mode
• show the active destination, folder, and recursion scope clearly
• avoid duplicate media when nested paths overlap
• keep folder search and switching responsive for large libraries
• support equivalent pointer, keyboard, screen-reader, and touch behavior on desktop and Android

Acceptance criteria

• selecting a folder never silently changes between direct-only and recursive results
• the active top-level Photos destination remains clear without a horizontally overflowing pill row
• mobile system back returns through folder/search context before leaving Photos
• desktop navigation supports keyboard focus and does not collapse into an enlarged phone layout
• grid and list views expose the same media and actions
• folder search can open a matching folder or filter the current scope
• recursive results remain incrementally paged and bounded in memory
• empty, inaccessible, renamed, moved, and deleted folders have explicit states
• overlapping nested folders do not duplicate media
• isolated fixtures and visual QA cover each recursion mode, both presentations, and compact/expanded navigation
• Android emulator and desktop tests cover navigation, back behavior, search, and preference restoration

Platforms

Android and desktop.