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, 4 insertions, 4 deletions

diff --git a/Hutch/Models/RepositorySummary.swift b/Hutch/Models/RepositorySummary.swift
index b41589b..40ec7a4 100644
--- a/Hutch/Models/RepositorySummary.swift
+++ b/Hutch/Models/RepositorySummary.swift
@@ -3,7 +3,7 @@ import Foundation
 /// Lightweight repository model matching the fields returned by the
 /// repositories list query. Avoids optionalizing all fields on the full
 /// `Repository` model.
-struct RepositorySummary: Codable, Sendable, Identifiable, Hashable {
+nonisolated struct RepositorySummary: Codable, Sendable, Identifiable, Hashable {
     let id: Int
     /// GraphQL resource identifier used by `repository(rid:)` queries.
     let rid: String
@@ -15,13 +15,13 @@ struct RepositorySummary: Codable, Sendable, Identifiable, Hashable {
     let owner: Entity
     let head: Reference?
 
-    enum CodingKeys: String, CodingKey {
+    nonisolated enum CodingKeys: String, CodingKey {
         case id, rid, service, name, description, visibility, updated, owner
         case head = "HEAD"
     }
 
     /// Grouped initializer fields (single parameter keeps APIs explicit without exceeding parameter-count limits).
-    struct Fields: Sendable, Hashable {
+    nonisolated struct Fields: Sendable, Hashable {
         let id: Int
         let rid: String
         let service: SRHTService
@@ -59,7 +59,7 @@ struct RepositorySummary: Codable, Sendable, Identifiable, Hashable {
     }
 }
 
-extension RepositorySummary {
+nonisolated extension RepositorySummary {
     var defaultBranchName: String? {
         head?.name.replacingOccurrences(of: "refs/heads/", with: "")
     }