Guide FSKit approval through category settings

[dbuskariol]

Summary

• replace the generic FSKit approval copy with the exact macOS category-based sequence
• make the recovery action explicitly open Login Items & Extensions
• bind the guidance to typed presentation and regression coverage
• synchronize README and production acceptance documentation

Root cause

On macOS 26.5.1, the app-grouped Delta Extensions switch did not persist FSKit approval. The category-specific File System Extensions control enabled the same registered module successfully, and Delta's FSClient status immediately changed to Allowed.

Verification

• focused Settings and Time Machine controller suite: 60 tests passed
• Scripts/verify-ci.sh: passed
• full Swift suite: 547 tests passed, 3 intentional opt-in skips
• real local restic and rclone integration lifecycles passed
• Release app, bundle signature, FSKit packaging, and fail-closed release checks passed