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/PairSheet.swift

@@ -39,12 +39,16 @@ struct PairSheet: View {
             Form {
                 Section {
                     TextField("PIN", text: $pin, prompt: Text("Shown in the host's log"))
-                        .font(.system(.body, design: .monospaced))
+                        .font(.system(.title3, design: .monospaced))
+                        #if os(iOS)
+                        .keyboardType(.numberPad)
+                        #endif
                     TextField(
                         "Client name", text: $clientName,
                         prompt: Text("How the host lists this Mac"))
                 } header: {
-                    Text("Pair with \(host.displayName)")
+                    Label("Pair with \(host.displayName)", systemImage: "lock.shield")
+                        .foregroundStyle(.tint)
                 } footer: {
                     Text("The host prints the PIN when pairing is armed "
                         + "(--allow-pairing, \u{201C}PAIRING ARMED\u{201D} in its log). "