Add Phase 2 TUI improvements: disk space checks and error hints
- Created internal/checks package for disk space and error classification
- CheckDiskSpace(): Real-time disk usage detection (80% warning, 95% critical)
- CheckDiskSpaceForRestore(): 4x archive size requirement calculation
- ClassifyError(): Smart error classification (ignorable/warning/critical/fatal)
- FormatErrorWithHint(): User-friendly error messages with actionable solutions
- Integrated disk checks into backup/restore workflows with pre-flight validation
- Error hints for: lock exhaustion, disk full, syntax errors, permissions, connections
- Blocks operations at 95% disk usage, warns at 80%
Renz
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