GiteaPR: native iOS app to manage Gitea pull requests

Multi-repo PR inbox, review (approve/request changes/comment), merge with
gating toggle, read-only diff viewer, and Gitea Actions check status with
one-tap re-run. Ships unsigned via the iMac runner to the SideStore source.

GiteaPR/Networking/APIError.swift

@@ -0,0 +1,32 @@
+import Foundation
+
+enum APIError: LocalizedError, Equatable {
+    case invalidURL
+    case invalidResponse
+    case httpStatus(Int, String?)
+    case decoding(String)
+    case unauthorized
+    case notFound
+
+    var errorDescription: String? {
+        switch self {
+        case .invalidURL:
+            return "The instance URL is invalid."
+        case .invalidResponse:
+            return "The server returned an invalid response."
+        case .httpStatus(let code, let message):
+            if code == 401 || code == 403 {
+                return "Authentication failed. Check your token."
+            }
+            return message?.isEmpty == false
+                ? "Server error (\(code)): \(message!)"
+                : "Server error (\(code))."
+        case .decoding(let detail):
+            return "Could not parse the server response: \(detail)"
+        case .unauthorized:
+            return "Authentication failed. Check your token."
+        case .notFound:
+            return "Not found."
+        }
+    }
+}