Add progress bars, fix DCT decode, sparkly MOTD

Progress bar support (v4.1.2):
- Web frontend: Real-time progress during encode with phase display
- CLI: --progress flag with rich library for encode command
- Backend: progress_file parameter for async progress reporting

DCT decode bug fix:
- Fixed InvalidMagicBytesError not being caught in early-exit check
- RS-protected format (v4.1.0+) has length prefix first, not magic bytes
- Exception handler now catches both ValueError and InvalidMagicBytesError

MOTD update:
- Added sparkly header to setup.sh MOTD (matches other rpi scripts)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

pyproject.toml

@@ -54,6 +54,7 @@ cli = [
     "click>=8.0.0",
     "qrcode>=7.30",
     "piexif>=1.1.0",
+    "rich>=13.0.0",
 ]
 compression = [
     "lz4>=4.0.0",