fix: debug No link returned on 13.140.132.105 - improve error reporting + timeout
- increase capture timeout 15->20s, keep output tail for diagnostics
- plugin_api: add _sshx_last_output/_last_error, /debug endpoint with arch/url/binary/platform
- /start now returns debug + output_tail on 500/504/202 so frontend shows real reason instead of 'No link returned'
- /status returns error+tail, installing/starting now shows message
- frontend: handle starting/installing/error with Debug view, show output_tail+debug JSON, refresh every 2.5s, Debug button
- __init__.py: same capture+error improvements for CLI tool
- bump v2.0.1