Add compress, rotate, convert tools to CLI

Port Web UI image tools to CLI for parity:
- compress: JPEG compression with size reduction stats
- rotate: Rotation and flip with jpegtran for JPEGs (DCT-safe)
- convert: Format conversion between PNG, JPG, BMP, WebP

Rotate tool supports flip-only operations without rotation.

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

TODO-4.2.1.md

@@ -18,7 +18,11 @@
   - Compress, Rotate, Strip, EXIF viewer all working
   - Rotate uses jpegtran for lossless JPEG rotation
   - Compact UI styling
-- [ ] CLI tools - full shakedown and fixes
+- [x] CLI tools - full shakedown and fixes
+  - Fixed encode to output JPEG when carrier is JPEG (was always PNG)
+  - Fixed jpegtran -trim flag destroying DCT stego data
+  - Added compress, rotate, convert tools (matching Web UI)
+  - Rotate uses jpegtran for JPEGs, supports flip-only operations
 
 ## AUR Packages
 - [ ] `stegasoo-cli` - standalone CLI package (no web dependencies)