Fix PR inbox: decode Gitea ISO8601 dates with timezone offset

Gitea returns dates like 2026-08-12T11:09:13+02:00. The default JSONDecoder
date strategy expects a Unix timestamp number, so decoding any Date? field
threw and the whole [PullRequest] array failed — the inbox showed no PRs.
Add a shared decoder with a custom ISO8601 strategy (with and without
fractional seconds) and use it for all get/post decoding.

GiteaPR/Networking/GiteaClient.swift

@@ -22,6 +22,32 @@ struct GiteaClient {
     let token: String
     let session: URLSession
 
+    /// Shared decoder. Gitea returns ISO8601 date strings WITH a timezone
+    /// offset (e.g. "2026-08-12T11:09:13+02:00"), which neither the default
+    /// `.deferredToDate` strategy (expects a Unix timestamp number) nor
+    /// `.iso8601` (expects a trailing "Z") can parse. Without this, decoding
+    /// any `Date?` field throws and the whole array fails — the inbox shows
+    /// nothing even though the data is present.
+    private static let decoder: JSONDecoder = {
+        let d = JSONDecoder()
+        let formatter = ISO8601DateFormatter()
+        formatter.formatOptions = [.withInternetDateTime,
+                                   .withFractionalSeconds]
+        d.dateDecodingStrategy = .custom { decoder in
+            let container = try decoder.singleValueContainer()
+            let str = try container.decode(String.self)
+            if let date = formatter.date(from: str) { return date }
+            // Fall back to a formatter without fractional seconds.
+            let plain = ISO8601DateFormatter()
+            plain.formatOptions = [.withInternetDateTime]
+            if let date = plain.date(from: str) { return date }
+            throw DecodingError.dataCorruptedError(
+                in: container,
+                debugDescription: "Cannot decode date string \(str)")
+        }
+        return d
+    }()
+
     init(instanceURL: URL, token: String, session: URLSession = .shared) {
         self.instanceURL = instanceURL
         self.token = token
@@ -62,7 +88,7 @@ struct GiteaClient {
         case 404:
             throw APIError.notFound
         default:
-            let message = (try? JSONDecoder().decode([String: String].self,
+            let message = (try? Self.decoder.decode([String: String].self,
                                                      from: data))?["message"]
             throw APIError.httpStatus(http.statusCode, message)
         }
@@ -72,7 +98,7 @@ struct GiteaClient {
                                    query: [URLQueryItem]? = nil) async throws -> T {
         let data = try await request(path, query: query)
         do {
-            return try JSONDecoder().decode(T.self, from: data)
+            return try Self.decoder.decode(T.self, from: data)
         } catch {
             throw APIError.decoding(String(describing: error))
         }
@@ -80,7 +106,7 @@ struct GiteaClient {
 
     private func post<T: Decodable>(_ path: String, body: Data? = nil) async throws -> T {
         let data = try await request(path, method: "POST", body: body)
-        return try JSONDecoder().decode(T.self, from: data)
+        return try Self.decoder.decode(T.self, from: data)
     }
 
     private func postNoBody(_ path: String) async throws {