Bump version to 4.2.1

Release highlights:
- API key authentication (X-API-Key header)
- TLS with self-signed certificates
- CLI tools: compress, rotate, convert
- jpegtran lossless JPEG rotation
- AUR packages: stegasoo-cli-git, stegasoo-api-git
- Bug fixes: DCT rotation, jpegtran -trim, CLI output format

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

src/stegasoo/__init__.py

@@ -7,7 +7,7 @@ Changes in v4.0.0:
 - encode() and decode() now accept channel_key parameter
 """
 
-__version__ = "4.2.0"
+__version__ = "4.2.1"
 
 # Core functionality
 # Channel key management (v4.0.0)

src/stegasoo/constants.py

@@ -31,7 +31,7 @@ from pathlib import Path
 # VERSION
 # ============================================================================
 
-__version__ = "4.2.0"
+__version__ = "4.2.1"
 
 # ============================================================================
 # FILE FORMAT