Add Android image storage and management parity

[catherineluse]

Background

Browser and Electron image management now use platform-specific storage behind shared image capabilities. Native Android image storage and UI support remain intentionally deferred.

Scope

• Implement a native image-content adapter for Capacitor Android.
• Store image bytes outside SQLite while retaining platform-neutral image IDs and metadata in SQLite.
• Enable selecting, viewing, downloading/sharing, replacing, and deleting book covers, part covers, and chapter images.
• Preserve rollback behavior when either blob or metadata persistence fails.
• Verify backup, restore, and legacy image migration behavior on Android.

Acceptance criteria

• Android exposes the appropriate image capability flags.
• Image CRUD survives app restart.
• Missing and quota/storage errors are actionable.
• Type-check, lint, automated coverage, and manual Android verification pass.