feat: add FileBookmarkService, BiometricAuthService, ClipboardService

Phase 3 (Tasks 10-11) app services: FileBookmarkService persists a
security-scoped bookmark for the KDBX file in the shared App Group;
BiometricAuthService wraps LAContext for Face ID/Touch ID; ClipboardService
copies text with an expiring clipboard entry on iOS/macOS.

Also fixes a real build issue found while verifying: the AutoFill
extension (iOS-only) was being embedded/signed unconditionally,
breaking macOS builds of the MyPass scheme with a bogus provisioning
error. Added platformFilters = (ios) to both the embed build file and
the target dependency so macOS builds skip it. Verified both iOS
Simulator and macOS builds now fail only on the known, expected
ContentView.swift/Item SwiftData breakage.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYqycDFsynHH9VnnK7LNSf

MyPass/Services/BiometricAuthService.swift

@@ -0,0 +1,23 @@
+//
+//  BiometricAuthService.swift
+//  MyPass
+//
+
+import LocalAuthentication
+import Foundation
+
+public final class BiometricAuthService {
+    public init() {}
+
+    public var isAvailable: Bool {
+        let ctx = LAContext()
+        var error: NSError?
+        return ctx.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)
+    }
+
+    /// Returns true on success. On failure, throws an error with a localized message.
+    public func authenticate(reason: String) async throws {
+        let ctx = LAContext()
+        try await ctx.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason)
+    }
+}