feat(xcode): safely clean XcodeBuildMCP DerivedData

[omartio]

What does this PR do?

Adds XcodeBuildMCP-managed DerivedData to PureMac Xcode Junk cleanup while preserving the existing cleanup safety contract.

• Discovers legacy and per-workspace XcodeBuildMCP DerivedData paths only.
• Requires explicit manual selection for XcodeBuildMCP DerivedData; rows are never auto-selected.
• Scheduled cleanup respects selection and additionally requires data older than 7 days without an active lifecycle lock. Scheduled scans leave MCP rows unselected.
• Re-checks and atomically acquires the workspace lifecycle lock before moving data to Trash.
• Keeps workspace logs, state, result bundles, test products, and locks intact.
• Canonicalizes symlinked homes consistently between scanning and cleaning.

Type of change

• Bug fix
• New feature
• Performance improvement
• UI/UX enhancement
• Documentation
• Other (describe)

Testing

• Tested on macOS Ventura (13.x)
• Tested on macOS Sonoma (14.x)
• Tested on macOS Sequoia (15.x)
• Full macOS test suite: 120 tests passed
• Regression coverage for manual selection, scheduled selection handling, recent data, active lifecycle locks, symlinked homes, and workspace state preservation

Screenshots

Not applicable.