TagoKoto

1. Capture & Import
   - Scan documents via camera with auto edge-detection, crop, perspective correction,
     and multi-page capture into a single PDF.
   - Import existing PDFs/images from device storage.
   - Save output as PDF or image (JPEG/PNG), user's choice.

2. Private, Hidden Storage
   - All saved files are stored in the app's private sandboxed storage directory —
     never in the public Camera Roll / Gallery / Downloads.
   - Files are excluded from:
     - Android: `MediaStore` indexing (no thumbnails in Gallery apps) and `.nomedia`
       enforcement at the directory level.
     - iOS: Files app visibility (no `UIFileSharingEnabled`), and never written to the
       Photos library.
   - Optional: encrypt files at rest (AES-256) so even a file-system-level snoop sees
     unreadable blobs.

3. Organization
   - Custom tags (multi-tag per document).
   - Folders/collections (optional layer on top of tags).
   - Full-text search across filenames, tags, and OCR'd document text.
   - Sort/filter by date, tag, type, size, favorite.

4. Viewing
   - In-app PDF viewer and image viewer (pinch-zoom, page navigation, rotate).
   - Thumbnail grid + list view toggle.

5. Security
   - App-level lock: PIN/passcode.
   - Biometric authentication (Face ID / Touch ID / Android BiometricPrompt) as an
     alternative/quick-unlock.
   - Per-document or per-folder lock: mark specific files "Private" requiring a second
     authentication step even after the app is unlocked.
   - Auto-lock on background/timeout.
   - Screenshot/screen-recording prevention on sensitive screens (`FLAG_SECURE` /
     iOS screen capture detection).