Add jpegtran lossless rotation and EXIF orientation handling

DCT steganography improvements:
- Add _apply_exif_orientation() to fix portrait photos encoding rotated
- Add _jpegtran_rotate() for lossless JPEG rotation preserving DCT data
- Add rotation fallback in extract_from_dct() - tries 0°, 90°, 180°, 270°
- Quick header validation to skip invalid rotations efficiently
- Fix: wrap debug.print in try/except to prevent extraction failures

Web UI rotate tool:
- Use jpegtran for JPEGs (lossless, preserves DCT steganography)
- Fall back to PIL for non-JPEGs
- Dynamic UI shows "DCT Safe" for JPEGs, warning for other formats

This enables the workflow: encode → compress → rotate → decode
Rotated stego JPEGs can now be decoded by trying all orientations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

TODO-4.2.1.md

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+# Stegasoo 4.2.1 Plan
+
+## Bugs
+- [ ] Fix EXIF viewer panel not loading metadata in Web UI
+- [x] DCT mode: portrait photos export rotated 90° (EXIF orientation not handled)
+  - Added `_apply_exif_orientation()` to apply EXIF rotation before embedding
+- [x] DCT mode: add rotation fallback (try as-is, rotate 90°, retry on failure)
+  - Added rotation fallback in `extract_from_dct()` with quick header validation
+- [x] Rotate tool: use jpegtran for lossless JPEG rotation (preserves DCT stego!)
+  - Web UI rotate tool now uses jpegtran for JPEGs
+  - DCT decode rotation fallback now uses jpegtran for JPEGs
+  - Dynamic UI shows "DCT Safe" for JPEGs, warning for other formats
+
+## Tools Audit
+- [ ] Web UI tools - full shakedown and fixes
+- [ ] CLI tools - full shakedown and fixes
+
+## AUR Packages
+- [ ] `stegasoo-cli` - standalone CLI package (no web dependencies)
+- [ ] `stegasoo-api` - REST API package (needs auth overhaul first)
+
+## API Auth Work (blocking stegasoo-api)
+- [ ] Implement OAuth2 authentication
+- [ ] TLS 1.3 support with self-signed certificates
+- [ ] Figure out cert trust/distribution for clients
+
+## API Documentation
+- [ ] Postman collection
+- [ ] Environment variable templates