[StanleyLl0yd]

Owner-requested repository-wide audit #145.

Exact starting main: d5906be1bf04139c673f2746954e8ed94d1502e4.

Scope: behavior-preserving simplification of the synchronous cancellation guards used by Tree, Search, Largest Files, and Sunburst derived presentation preprocessors.

• Replace four identical withUnsafeCurrentTask { task in task?.isCancelled ?? false } computed properties with the standard Swift 6 Task.isCancelled access at the existing guard sites.
• Preserve existing short-circuit positions and nil/cancellation contracts; do not change async state machines or UI behavior.
• Add a focused test that cancels the current detached task and asserts all four preprocessors return nil rather than publishing work.
• Independent Linux Swift 6.2.1 syntax/semantics probe showed equality of both cancellation reads outside a task and within a cancelled task. This is supplementary only; macOS Xcode 26.6 XCTest and CodeQL are decisive.

Exactly three changed files: ContentView.swift, Utilities.swift, DiskUsageTests/FolderUsageTests.swift.
No scanner, model, filesystem, Trash, resource, release, CI, dependency or roadmap change.

Hold merge until prior #149 exact-main is fully green, and this PR's own exact-head CI/Security/Dependency Review/CodeQL Actions+Swift and zero review threads pass. Verify merged main afterward.