Add UPX compression - 80% binary size reduction

Binary size: 5.1MB → 1.6MB (stripped + UPX --best --lzma)

Changes:
- Updated binary with UPX compression
- Added UPX to GitHub Actions build workflow
- Documented UPX compression in README and BUILD.md
- No functionality loss, no performance penalty
- Decompresses automatically on execution

Benefits:
- Faster downloads
- Less storage/bandwidth usage
- Same performance (decompresses to RAM)
- Fully reversible (upx -d)

README.md

@@ -33,12 +33,14 @@ sudo ./install.sh
 
 ## What's Included
 
-- **trianglesd** v5.4.4 - Native ARM64 binary (85MB)
+- **trianglesd** v5.4.4 - Native ARM64 binary (1.6MB, UPX compressed)
 - **Tor integration** - Built-in hidden service support
 - **Updated seed nodes** - Latest v5.4.4 onion addresses
 - **Auto-installer** - One-command setup
 - **Full documentation** - Build instructions and usage guide
 
+**Note:** Binary is compressed with UPX (Ultimate Packer for Executables) for 80% size reduction. Decompresses automatically on execution with no performance penalty.
+
 ## System Requirements
 
 - **Platform:** Raspberry Pi 4/5 (64-bit) or any ARM64 Linux server