Add support for browser bookmarks

Summary

Add persistent bookmarks with folders and a native Photon bookmarks page.

Scope

• Add a validated, profile-scoped bookmark model and atomic storage.
• Support adding the current page, editing its title/address, moving it, and deleting it.
• Provide a native photon://bookmarks page with folders, search, and useful empty states.
• Keep bookmarks distinct from pinned tabs and space favourites.
• Reuse saved page icons where available and expose bookmarks to the existing command bar.

Acceptance criteria

• Bookmark edits survive restart and malformed profile data cannot break the bookmark store.
• Duplicate addresses have predictable behavior.
• Folder operations and bookmark search work from the native page and command bar.

Design reference: Zephium keeps bookmarks separate from live pinned tabs and represents imported trees with validated core contracts: https://github.com/zephium-browser/Zephium/blob/main/crates/zephium-core/src/bookmarks.rs