feat(ios): replace embedded website with initial native SwiftUI API client

Introduce real SwiftUI auth/dashboard/task/note/shopping screens, a bounded origin-bound URLSession transport and Keychain-backed native sessions. Archive the rejected WebKit renderer rather than embedding it for unfinished modules. Sixteen portable URL/contract/transport tests and Swift format/parsing pass on Linux; Apple SDK application and UI validation remains mandatory. This is an incomplete native slice, not full PWA parity or a release.

ios/Sources/NativeSessionVault.swift

@@ -0,0 +1,40 @@
+import Foundation
+import Security
+
+/// Native cookies, separate from WebKit and scoped to one configured origin.
+struct NativeSessionVault: Sendable {
+    let origin: String
+    private var query: [String: Any] {
+        [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: "community.yuvomi.mobile.native-session",
+            kSecAttrAccount as String: origin,
+        ]
+    }
+    func load() -> Data? {
+        var request = query
+        request[kSecReturnData as String] = true
+        request[kSecMatchLimit as String] = kSecMatchLimitOne
+        var result: CFTypeRef?
+        guard SecItemCopyMatching(request as CFDictionary, &result) == errSecSuccess else { return nil }
+        return result as? Data
+    }
+    func save(_ data: Data) throws {
+        let attributes: [String: Any] = [
+            kSecValueData as String: data,
+            kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly,
+        ]
+        let status = SecItemUpdate(query as CFDictionary, attributes as CFDictionary)
+        if status == errSecItemNotFound {
+            var request = query
+            for (key, value) in attributes { request[key] = value }
+            guard SecItemAdd(request as CFDictionary, nil) == errSecSuccess else { throw NativeAPIError.unavailable }
+        } else if status != errSecSuccess {
+            throw NativeAPIError.unavailable
+        }
+    }
+    func clear() throws {
+        let status = SecItemDelete(query as CFDictionary)
+        guard status == errSecSuccess || status == errSecItemNotFound else { throw NativeAPIError.unavailable }
+    }
+}