fix(quic/apple): QUIC keep-alive + reconnect input re-engage

Three native-client bugs isolated against a stock Moonlight client (which
stays connected / keeps input working under the same actions):

- Connection drops mid-stream: the quinn endpoints (host + client) ran with
  default transport config, so keep_alive_interval was OFF. Any quiet stretch
  (no input, audio muted/stalled, a capture hiccup, a mode change) let the
  idle timer expire and quinn closed the session -> next_au=Closed -> "Session
  ended". Moonlight's ENet sends keepalive pings; we sent nothing. Add a shared
  TransportConfig (keep-alive 4s under an explicit 20s idle timeout) to both
  endpoint::server_from_der and endpoint::client_pinned_with_identity.

- Reconnect input dead (macOS): the session-start auto-capture one-shot was
  consumed even when engageCapture(fromClick:false) was refused (window not key
  yet at the instant of reconnect), with no retry -> capture stayed off and
  input never forwarded. Clear the one-shot only on a successful engage, and
  retry on NSWindow.didBecomeKey. Stays scoped to session start, so it does not
  resurrect the rejected auto-grab-on-activation behavior.

- Reconnect input dead (iOS): wasCapturedOnResign leaked stale state across
  sessions and the foreground-restore could fire before this session's
  InputCapture was wired (setForwarding no-ops on nil). Reset it per session in
  start() and guard the didBecomeActive restore on inputCapture != nil.

Validated: cargo build -p punktfunk-core --features quic; swift build;
swift test (39 passed, 0 failures); xcframework rebuilt (all 5 slices), no
ABI/header drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkKit/StreamViewIOS.swift

@@ -172,6 +172,10 @@ public final class StreamViewController: UIViewController {
         self.connection = connection
         loadViewIfNeeded()
         #if os(iOS)
+        // Fresh session: drop any resign/foreground capture-restore state left over from a
+        // prior session (stop() doesn't clear it). Otherwise a stale `true` could later
+        // re-engage capture on a foreground that the new session never asked for.
+        wasCapturedOnResign = false
         // Read the LIVE mode per touch batch — an accepted requestMode() mid-stream
         // changes the letterbox, and touches must follow it.
         streamView.currentHostMode = { [weak connection] in
@@ -247,7 +251,10 @@ public final class StreamViewController: UIViewController {
         observers.append(NotificationCenter.default.addObserver(
             forName: UIApplication.didBecomeActiveNotification, object: nil, queue: .main
         ) { [weak self] _ in
-            guard let self, self.wasCapturedOnResign, self.captureEnabled, self.connection != nil
+            // inputCapture != nil: don't try to restore before this session's capture is wired
+            // up — setForwarding would silently no-op on the nil handlers and leave input dead.
+            guard let self, self.wasCapturedOnResign, self.captureEnabled,
+                  self.connection != nil, self.inputCapture != nil
             else { return }
             self.setCaptured(true)
         })