feat(mh3g): split compatibility repair by data domain

[VincentAdamNemessisX]

Summary

• split compatibility repair into independently authorized core, guild-card, quest, shared-system, and experimental CEC transactions
• add explicit original 3DS, read-only current Wii U/Cemu, and independent output paths for every domain in both native UIs
• preserve continued-play Wii U data: historical three-way repair for core/cards, exact current-byte preservation for quests, verified flag union for system, and exact-record/empty-slot repair for CEC
• give every domain its own Dry Run fingerprint, write gate, manifest, and rollback; an incomplete or failed optional domain no longer blocks/revokes another
• retain the legacy coupled repair-converted --source-extdata-dir CLI option for existing scripts, while native UIs use only the new domain-scoped commands
• document exact path/file/group contracts and add ADR 0017

Validation

• cargo fmt --all -- --check
• cargo test -p mh3g-save-convert — 224 passed
• cargo clippy -p mh3g-save-convert --all-targets -- -D warnings
• cargo clippy -p mh3g-save-convert --target x86_64-pc-windows-msvc --all-targets -- -D warnings
• swift test — 76 passed
• python3 scripts/mh3g-docs-contract.py
• python3 scripts/verify-mh3g-save-converter-windows-source.py
• bash scripts/build-mh3g-save-converter-macos-app.sh
• bash scripts/mh3g-save-converter-macos-smoke.sh
• direct macOS app UI inspection: repair mode shows separate core source/current/output; system source/current/output; ExtData source/current/output; independent card/quest transactions
• paired real-hardware user1/ExtData/Wii U fixture: core exact 0.0.5; cards compatible 0.0.5-0.0.6; quests compatible 0.0.3-0.0.6; all three written and rolled back independently; all 3DS/current-reference payload hashes remained unchanged and all output payloads restored exactly

Boundaries

• no Cemu/game runtime validation was performed
• no formal native WinUI build was performed on macOS; Windows source/XAML contract and Rust MSVC target lint passed, native Windows build remains a Windows release/tester gate
• no production Nemessix/Azahar/Cemu save or MLC was modified
• PR fix(mh3g): clarify accepted save path structures #39 remains separately owned and is not included here

[VincentAdamNemessisX]

Lifecycle audit: this PR is not merged or superseded. The independent repair commands remain absent from current main, while its WinUI layer conflicts with the Fluent rewrite merged in #42. Keep open; preserve the Rust/macOS/docs work and rebase or re-implement the Windows UI against current main (preferably after #44). Do not force-merge the stale XAML.