feat(apple): styling pass — dark-mode accent, recent-host state, glass HUD, security-sheet polish

Working through the brand-color follow-ups:

- AccentColor gains a dark-appearance variant (#8678F5 — the brand violet lifted one
  step toward the icon's light periwinkle) so tinted controls keep contrast on dark.
- Host cards remember sessions: StoredHost.lastConnected (set when a session reaches
  streaming) renders as a "Connected … ago" relative-time line, and the most recent
  host's card carries a subtle accent ring — the grid finally has hierarchy.
- The HUD swaps the pre-glass black-50% rectangle for .regularMaterial with an accent
  live-dot; hint lines use semantic .secondary instead of opacity.
- Security moments: the trust card's lock.shield and the pairing sheet's header take
  the brand tint; the PIN field is larger monospaced and uses the number pad on iOS.

Icon ↔ accent decision: the accent stays the exact brand #6656F2; the Icon Composer
layers keep their adjacent palette (#6C5BF3 family) — close enough to read as one
brand, and the icon remains the design-tool source of truth.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/HostStore.swift

@@ -18,6 +18,8 @@ struct StoredHost: Identifiable, Codable, Hashable {
     var port: UInt16 = 9777
     /// SHA-256 of the host's certificate, set after the user explicitly trusted it.
     var pinnedSHA256: Data?
+    /// Last time a streaming session actually started (nil until the first one).
+    var lastConnected: Date?
 
     var displayName: String { name.isEmpty ? address : name }
 }
@@ -47,6 +49,11 @@ final class HostStore: ObservableObject {
         hosts.removeAll { $0.id == host.id }
     }
 
+    func markConnected(_ hostID: UUID) {
+        guard let i = hosts.firstIndex(where: { $0.id == hostID }) else { return }
+        hosts[i].lastConnected = Date()
+    }
+
     func pin(_ hostID: UUID, fingerprint: Data) {
         guard let i = hosts.firstIndex(where: { $0.id == hostID }) else { return }
         hosts[i].pinnedSHA256 = fingerprint