[TASK] ScanItem sum-type + CleanAction sum-type + SymlinkPolicy

[kirich1409]

Context

Public value types expressing scan output and clean actions.

Acceptance criteria

• ScanItem covers .file / .directory / .externalResource / .archivable.
• CleanAction covers .trash / .archive / .externalCommand / .hint.
• SymlinkPolicy enum present (rejectIfSymlink / trashSymlinkOnly / trashTargetRequireSafe).
• All Sendable + Codable where applicable.

Files to touch (estimate)

best-effort estimate; agent refines during implementation

Implementation notes

n/a

Dependencies

None.

Safety checklist

See .github/ISSUE_TEMPLATE/task.yml — tick applicable invariants in the issue if any destructive path is touched.

Definition of Done

• Acceptance criteria satisfied and verifiable
• Tests added or updated
• No build / lint / test regressions
• Self-review against research-report invariants
• Code review approved