Drop App Groups, share via keychain access group only

Apple's ASC API doesn't expose App Group registration cleanly, and the
keychain access group on its own (`$(AppIdentifierPrefix)<bundleId>`)
already gives the share extension and container app a shared store for
the base URL + token. The repo cache moves to per-process UserDefaults —
the extension fetches/caches it on first share if empty.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Shared/RepoCache.swift

@@ -9,7 +9,7 @@ enum RepoCache {
 
     static var repos: [GiteaRepo] {
         get {
-            guard let data = AppSettings.sharedDefaults.data(forKey: listKey) else { return [] }
+            guard let data = AppSettings.localDefaults.data(forKey: listKey) else { return [] }
             let decoder = JSONDecoder()
             decoder.dateDecodingStrategy = .iso8601
             return (try? decoder.decode([GiteaRepo].self, from: data)) ?? []
@@ -18,14 +18,14 @@ enum RepoCache {
             let encoder = JSONEncoder()
             encoder.dateEncodingStrategy = .iso8601
             if let data = try? encoder.encode(newValue) {
-                AppSettings.sharedDefaults.set(data, forKey: listKey)
-                AppSettings.sharedDefaults.set(Date(), forKey: listFetchedKey)
+                AppSettings.localDefaults.set(data, forKey: listKey)
+                AppSettings.localDefaults.set(Date(), forKey: listFetchedKey)
             }
         }
     }
 
     static var fetchedAt: Date? {
-        AppSettings.sharedDefaults.object(forKey: listFetchedKey) as? Date
+        AppSettings.localDefaults.object(forKey: listFetchedKey) as? Date
     }
 
     static var isStale: Bool {
@@ -34,13 +34,13 @@ enum RepoCache {
     }
 
     static var recentFullNames: [String] {
-        AppSettings.sharedDefaults.stringArray(forKey: recentsKey) ?? []
+        AppSettings.localDefaults.stringArray(forKey: recentsKey) ?? []
     }
 
     static func touch(_ fullName: String) {
         var current = recentFullNames.filter { $0 != fullName }
         current.insert(fullName, at: 0)
         if current.count > recentsCap { current = Array(current.prefix(recentsCap)) }
-        AppSettings.sharedDefaults.set(current, forKey: recentsKey)
+        AppSettings.localDefaults.set(current, forKey: recentsKey)
     }
 }