Add unified Xbox Package Lab

[TrapEmAll]

Summary

• add a unified Package Lab page to the sidebar and Tools menu
• move STFS/XBE/XEX ownership into the packages domain
• support fragmented STFS chains, extraction, SHA-1 verification, transactional replacement, metadata edits, rehashing, and caller-supplied signing callbacks
• add SVOD/GoD inventory, verification, and payload reconstruction
• add GDF/XISO inventory and safe extraction
• add FATX image partition browsing, extraction, and guarded same-allocation replacement into a separate image
• add transactional GPD achievement and setting edits in the profiles domain
• document format coverage, safety limits, attribution, and deliberate exclusions

Verification

• python -m ruff check .
• python tests.py (137 passed)
• Package Lab import smoke test
• synthetic round trips for fragmented STFS, tamper detection, GDF/XISO, SVOD, FATX, and GPD

Safety and provenance

All writes stage through temporary files. FATX/GPD edits require separate outputs; STFS and FATX replacement cannot exceed existing allocations. UnityScraper does not bundle X360 private key resources, updater/artwork, account credential modification, or DLC license-bypass behavior. Format geometry is attributed to Dalavin/DJ SkunkieButt's GPLv3 X360 source.