gather-info: add security, reliability, and diagnostic improvements

- Make full journal and container logs opt-in (--include-full-journal, --include-container-logs)
- Add timeout wrappers to prevent hanging on slow commands
- Add secret sanitization for network configs and process lists
- Fix docker sanitization fallback to never leak sensitive data
- Add GPU error collection (Xid, ECC, throttle, PCIe status)
- Add OOM detection, storage health, and InfiniBand support
- Enhance summary with auto-detected issues
- Fix grep -P portability bug
- Add disk space validation before collection

Author: Banshee1221