feat: Add configurable default bookmark list view

[ajaypremshankar]

Closes #141

Adds a user-configurable "Default view" setting that controls which bookmark filter is active when the app
starts. Previously, the app always opened to the "All" view. Users can now choose from:

• All (default, preserves existing behaviour)
• Unread
• Archive
• Favorites

The setting is available under Settings > User Interface > Default view.

Additionally, the top app bar title on the bookmark list screen now dynamically reflects the active filter
(e.g., "Unread", "Favorites") instead of always showing "Bookmarks".

Changes

• New DefaultFilter preference persisted via EncryptedSharedPreferences, loaded on startup to set the
  initial bookmark list filter
• "Default view" setting in the UI Settings screen with a radio-button dialog, following the existing Theme
  dialog pattern
• Top app bar title on the bookmark list screen now dynamically reflects the active filter instead of
  always showing "Bookmarks"
• Fixed a pre-existing bug where the initial sync check was unreachable due to placement after an infinite
  flow collector

Screenshots

Test plan

• Fresh install opens on "All" (backwards compatible)
• Change default to "Unread" → restart app → lands on "Unread", drawer highlights "Unread", title shows
  "Unread"
• Repeat for "Archive" and "Favourites"
• Switch back to "All" → restart → original behaviour restored
• Manually switching filters via the drawer still works regardless of the default setting
• Shared text intent still opens the create-bookmark dialogue regardless of the default filter
• Setting persists across app restarts

[ajaypremshankar]

@jensomato thanks for maintaining this app. Has given me such a peaceful way of reading. It just fits right in.

Here's a small contribution from my side. Hope we can action this. Thank you.

[jensomato]

Many thanks for your contribution. Could you look into the failing unit tests in BookmarkListViewModelTest