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/StreamView.swift

@@ -197,6 +197,17 @@ public final class StreamLayerView: NSView {
                 self?.releaseCapture()
             })
         }
+        // Becoming key RETRIES a still-pending session-start auto-capture — the case where a
+        // session began (reconnect) while this window wasn't key yet, so engageCapture(fromClick:
+        // false) was refused by its key-window guard and, with no retry, capture stayed off and
+        // input dead. This is a no-op once capture engaged (pendingAutoCapture is cleared) and
+        // after a manual ⌘⎋/focus-loss release (the flag is already false), so it does NOT
+        // resurrect the deliberately-rejected "auto-grab on every activation" behavior.
+        windowObservers.append(NotificationCenter.default.addObserver(
+            forName: NSWindow.didBecomeKeyNotification, object: window, queue: .main
+        ) { [weak self] _ in
+            self?.attemptPendingCapture()
+        })
         attemptPendingCapture()
     }
 
@@ -301,8 +312,13 @@ public final class StreamLayerView: NSView {
 
     private func attemptPendingCapture() {
         guard pendingAutoCapture, window != nil, bounds.width > 0 else { return }
-        pendingAutoCapture = false // one shot, even if the engage below is refused
         engageCapture(fromClick: false)
+        // Clear the one-shot only once it ACTUALLY engaged. If the engage was refused — the
+        // app/window isn't key yet (common right after a reconnect), or the cursor grab raced
+        // app activation — leave it armed so didBecomeKey (or the next layout pass) retries.
+        // This stays scoped to session start: a later manual release (⌘⎋, focus loss) doesn't
+        // re-arm it, so it never resurrects auto-grab-on-activation.
+        if captured { pendingAutoCapture = false }
     }
 
     private func engageCapture(fromClick: Bool) {