feat(ios): device client-cert mTLS — ClientTLS package, transport wiring, install UX (C-iOS)

- ios/Packages/ClientTLS: SecIdentity wrapper, PKCS12 importer (typed errors), keychain store
  (AfterFirstUnlockThisDeviceOnly), pure MutualTLSChallengeResponder truth table, cross-platform
  X.509 DER summary. 14/14 tests.
- Both transports (SessionCore URLSessionTermTransport, App URLSessionHTTPTransport) + SessionThumbnail
  take a lazy @Sendable ()->ClientIdentity? provider: WS resolves per-connect, HTTP per client-cert
  challenge, so a freshly-imported cert applies without an app relaunch. AppEnvironment injects
  { store.loadedIdentityOrNil() }.
- ClientCertScreen (.fileImporter([.pkcs12]) + passphrase -> import -> keychain), reachable via a
  设备证书 entry in SessionListScreen.hostMenu. PairingViewModel gates tunnel-host probes on cert
  presence and re-maps mTLS-reject to a clientCertRejected message.
Verified: ClientTLS 14/14, SessionCore 93/93, xcodegen + xcodebuild BUILD SUCCEEDED.

ios/Packages/ClientTLS/Tests/ClientTLSTests/PKCS12ImporterTests.swift

@@ -0,0 +1,69 @@
+import Foundation
+import Security
+import Testing
+@testable import ClientTLS
+
+// C-iOS-1 · PKCS#12 import against a real OpenSSL-generated fixture `.p12`,
+// including the wrong-passphrase and corrupt-file error mappings.
+
+@Test("import with the correct passphrase yields an identity whose leaf CN matches")
+func importSucceedsAndExposesLeaf() throws {
+    // Arrange
+    let data = ClientTLSFixtures.deviceP12Data
+
+    // Act
+    let identity = try PKCS12Importer.importIdentity(
+        data: data, passphrase: ClientTLSFixtures.passphrase
+    )
+
+    // Assert
+    let summary = try #require(identity.summary())
+    #expect(summary.subjectCommonName == ClientTLSFixtures.leafCommonName)
+    #expect(summary.issuerCommonName == ClientTLSFixtures.issuerCommonName)
+    // 825-day leaf minted at authoring time → not yet expired.
+    #expect(summary.isExpired() == false)
+}
+
+@Test("import drops the leaf from the issuer chain (credential must not repeat it)")
+func importIssuerChainExcludesLeaf() throws {
+    // Arrange / Act
+    let identity = try PKCS12Importer.importIdentity(
+        data: ClientTLSFixtures.deviceP12Data, passphrase: ClientTLSFixtures.passphrase
+    )
+
+    // Assert — fixture chain is [leaf, CA]; issuerCertificates keeps only the CA.
+    let leaf = try #require(identity.leafCertificate())
+    let leafData = SecCertificateCopyData(leaf) as Data
+    #expect(identity.issuerCertificates.count == 1)
+    for issuer in identity.issuerCertificates {
+        #expect((SecCertificateCopyData(issuer) as Data) != leafData)
+    }
+}
+
+@Test("wrong passphrase maps errSecAuthFailed → .wrongPassphrase")
+func importWrongPassphrase() {
+    // Arrange / Act / Assert
+    #expect(throws: PKCS12ImportError.wrongPassphrase) {
+        _ = try PKCS12Importer.importIdentity(
+            data: ClientTLSFixtures.deviceP12Data, passphrase: "not-the-passphrase"
+        )
+    }
+}
+
+@Test("garbage bytes map errSecDecode → .corruptFile")
+func importCorruptFile() {
+    // Arrange
+    let garbage = Data([0x00, 0x01, 0x02, 0x03, 0x99, 0xAB, 0xCD, 0xEF])
+
+    // Act / Assert
+    #expect(throws: PKCS12ImportError.corruptFile) {
+        _ = try PKCS12Importer.importIdentity(data: garbage, passphrase: "x")
+    }
+}
+
+@Test("empty data is treated as a corrupt file, not a crash")
+func importEmptyData() {
+    #expect(throws: PKCS12ImportError.corruptFile) {
+        _ = try PKCS12Importer.importIdentity(data: Data(), passphrase: "x")
+    }
+}