Adopt Swift 6 language mode

Flip SWIFT_VERSION to 6.0 (keeping SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor)
and resolve every resulting diagnostic. Mechanical, no behaviour change:

- Models: pure value types in Models/ and utility extensions (Date, DateFormatter,
  SRHTWebURL) marked nonisolated so the nonisolated networking layer can use them.
- App Intents: stored 'static var' (title/description/openAppWhenRun/
  typeDisplayRepresentation/defaultQuery/caseDisplayRepresentations) -> 'static let';
  drop the invalid @retroactive on the in-module LookupType: AppEnum.
- Sendable dicts: 'nil as String? as Any' -> 'nil as String? as any Sendable'.
- UserDefaults: retroactive @unchecked Sendable (documented thread-safe).
- WidgetKit completion handlers rebound nonisolated(unsafe) to cross into Task {};
  TipStoreViewModel task handle is @ObservationIgnored nonisolated(unsafe) for
  its nonisolated deinit.
- Tests run on @MainActor; a few constant fixtures marked nonisolated for use in
  @Sendable stub closures.

Builds and the full suite are clean in Swift 6 mode. Roadmap updated.

1 files changed, 8 insertions, 8 deletions

diff --git a/Hutch/Models/CommitDetail.swift b/Hutch/Models/CommitDetail.swift
index c95199d..962d2a4 100644
--- a/Hutch/Models/CommitDetail.swift
+++ b/Hutch/Models/CommitDetail.swift
@@ -1,7 +1,7 @@
 import Foundation
 
 /// Full commit detail returned by the revparse_single query.
-struct CommitDetail: Codable, Sendable, Identifiable {
+nonisolated struct CommitDetail: Codable, Sendable, Identifiable {
     let id: String
     let shortId: String
     let author: CommitAuthor
@@ -26,39 +26,39 @@ struct CommitDetail: Codable, Sendable, Identifiable {
     }
 }
 
-struct CommitTrailer: Codable, Sendable, Identifiable {
+nonisolated struct CommitTrailer: Codable, Sendable, Identifiable {
     var id: String { "\(name):\(value)" }
     let name: String
     let value: String
 }
 
-struct ParentCommit: Codable, Sendable, Identifiable, Hashable {
+nonisolated struct ParentCommit: Codable, Sendable, Identifiable, Hashable {
     let id: String
     let shortId: String
     let author: ParentAuthor
 }
 
-struct ParentAuthor: Codable, Sendable, Hashable {
+nonisolated struct ParentAuthor: Codable, Sendable, Hashable {
     let name: String
 }
 
-struct CommitTree: Codable, Sendable {
+nonisolated struct CommitTree: Codable, Sendable {
     let entries: CommitTreeEntries
 }
 
-struct CommitTreeEntries: Codable, Sendable {
+nonisolated struct CommitTreeEntries: Codable, Sendable {
     let results: [CommitTreeEntry]
     let cursor: String?
 }
 
-struct CommitTreeEntry: Codable, Sendable, Identifiable {
+nonisolated struct CommitTreeEntry: Codable, Sendable, Identifiable {
     let id: String
     let name: String
     let mode: Int
     let object: CommitTreeObject?
 }
 
-struct CommitTreeObject: Codable, Sendable {
+nonisolated struct CommitTreeObject: Codable, Sendable {
     let type: String?
     let id: String?
     let shortId: String?