Add export/import of redaction settings as a shareable JSON profile

[LegalMarc]

Goal

Let a user export their MetadataCleaningSettings and RedactionSettings as a JSON file, and import one, so legal teams can share a standard configuration profile.

Dependencies

None — immediately eligible.

Scope

• Make MetadataCleaningSettings and RedactionSettings (find their definitions in src/swift/MarcutApp/Sources/MarcutApp/ — likely DocumentModels.swift or similar) Codable if not already.
• Add "Export Profile..." and "Import Profile..." actions to SettingsView.swift using NSSavePanel/NSOpenPanel (this is a sandboxed macOS app — use the existing file-access patterns already in the codebase, e.g. how FileAccessCoordinator.swift handles user-selected file access, rather than introducing a new pattern).
• Export writes a single JSON file combining both settings structs under named top-level keys (e.g. {"metadataCleaningSettings": {...}, "redactionSettings": {...}}) with a schemaVersion field for forward compatibility.
• Import reads that JSON, validates the schemaVersion, and applies both settings structs, replacing current values. Reject/error clearly on a malformed or wrong-schema-version file rather than partially applying it.

Out of scope

• Cloud sync or automatic profile distribution — this is local file export/import only.
• Merging an imported profile with existing settings — import always fully replaces.

Acceptance criteria

• Exporting produces a JSON file containing both settings structs and a schema version.
• Importing that same file into a fresh settings state reproduces the original values exactly.
• Importing a malformed JSON file or one with an unrecognized schema version shows a clear error and does not change any current settings.

Required verification

• swift build --package-path src/swift/MarcutApp — must succeed.
• swift test --package-path src/swift/MarcutApp — all existing tests must still pass.
• Add round-trip tests: encode a settings pair to JSON, decode it back, assert equality; and a test that decoding a malformed/wrong-version payload throws/fails cleanly without mutating any passed-in state.

Notes

• Read FileAccessCoordinator.swift before adding file-picker code — the app is sandboxed and already has a pattern for user-selected file access that should be reused, not duplicated.

[LegalMarc]

Implemented in 66543a2. Review approved (independent reviewer). Acceptance criteria: all passed — RedactionProfile (schema-versioned, Codable) plus Export Profile…/Import Profile… controls in SettingsView let users export current settings to JSON and import a shared profile, with round-trip and malformed/unsupported-schema tests added in MarcutAppTests.swift.