feat: server config, token client, TLS pinning, connection test (Phase 1)

ServerConfig parses https base URL and derives wss livekit URL;
TokenClient POSTs /token with clean 503/offline error states;
TLSPinning holds optional cert SHA-384 pins (empty = system trust);
Settings gains a Connection test screen proving the endpoint works.

Sources/Features/Settings/ConnectionTestView.swift

@@ -0,0 +1,86 @@
+import SwiftUI
+
+struct ConnectionTestView: View {
+    @ObservedObject var settings: SettingsStore
+    @State private var isBusy = false
+    @State private var result: Result<TokenResponse, Error>?
+    @State private var urlError: String?
+
+    var body: some View {
+        Form {
+            Section("Server") {
+                LabeledContent("URL") {
+                    Text(settings.trimmedServerURL)
+                        .font(.footnote.monospaced())
+                        .foregroundStyle(.secondary)
+                }
+                if let urlError {
+                    Label(urlError, systemImage: "xmark.octagon")
+                        .foregroundStyle(.red)
+                }
+            }
+            Section {
+                Button(action: runTest) {
+                    HStack {
+                        Spacer()
+                        if isBusy {
+                            ProgressView()
+                        } else {
+                            Text("Get token")
+                        }
+                        Spacer()
+                    }
+                }
+                .disabled(isBusy || settings.trimmedServerURL.isEmpty)
+            }
+            if let result {
+                switch result {
+                case .success(let response):
+                    Section("Success") {
+                        LabeledContent("Room") {
+                            Text(response.room)
+                                .font(.footnote.monospaced())
+                        }
+                        LabeledContent("User") {
+                            Text(response.user.displayName ?? response.user.id)
+                        }
+                        Label("Token endpoint and TLS are working.", systemImage: "checkmark.circle")
+                            .foregroundStyle(.green)
+                    }
+                case .failure(let error):
+                    Section("Error") {
+                        Label(error.localizedDescription, systemImage: "xmark.octagon")
+                            .foregroundStyle(.red)
+                            .font(.footnote)
+                    }
+                }
+            }
+        }
+        .navigationTitle("Connection test")
+    }
+
+    private func runTest() {
+        result = nil
+        urlError = nil
+        switch ServerConfig.parse(settings.trimmedServerURL) {
+        case .success(let config):
+            isBusy = true
+            Task {
+                let client = TokenClient(config: config)
+                do {
+                    let response = try await client.fetchToken()
+                    result = .success(response)
+                } catch {
+                    result = .failure(error)
+                }
+                isBusy = false
+            }
+        case .failure(let error):
+            urlError = error.localizedDescription
+        }
+    }
+}
+
+#Preview {
+    ConnectionTestView(settings: SettingsStore())
+}