refactor: simplify install script by 73% (529 → 143 lines)

Major simplifications:
- Combine dependency checks into single function
- Remove OS-specific auto-installation code
- Remove elaborate PATH detection (pipx handles it)
- Simplify error handling and logging
- Condense functions with one-liner utilities
- Remove redundant version checking

Still maintains:
- All core functionality (download, extract, install)
- Proper error handling and cleanup
- Version tracking and CLI arguments
- Help documentation

Result: 73% smaller, much easier to maintain, still fully functional

scripts/install.sh

@@ -138,3 +138,7 @@ Usage:
 
 Update:
   curl -fsSL https://raw.githubusercontent.com/$REPO_OWNER/$REPO_NAME/main/scripts/install.sh | bash
+EOF
+}
+
+main "$@"