refactor: isolate application availability probing

[ygsgdbd]

Summary

Rule model properties previously probed the file system whenever menu classification or app information was read, making business tests depend on real directories. Introduce an injectable AppAvailabilityClient and an in-memory path snapshot so these projections read explicit availability results.

Refresh the snapshot at startup and on each new menu presentation. Rule cleanup probes again before deleting, preserving apps restored since the menu opened and all ignored rules. A changed path cannot reuse its previous result. Persisted rule fields remain unchanged, and README demo availability is deterministic.

Testing

• Added regression coverage for menu reopening, cleanup after apps are restored or removed, ignored-rule protection, and changed-path invalidation.
• Kept a live file-system adapter test for directory creation and removal; business tests use controlled availability.
• Verified README demo menu presentation does not probe the live file system.
• Full XCTest suite after rebasing onto current main: 141 tests passed, 0 failures.
• Pinned SwiftFormat 0.62.1 and git diff --check passed.

Changelog

• Updated both Chinese and English entries under Unreleased in CHANGELOG.md.
• No changelog entry is needed. Reason: Internal dependency and snapshot refactor; existing availability criteria and stored rule format are preserved.

Privacy

• This change does not add telemetry or upload user data, or the reason this is not applicable is explained above.