feat(apple): explicit input-capture state machine — no more cursor grabs on window chrome

Capture used to engage whenever the app became active, so the click that activates the
window — on the title bar (a drag) or a resize edge — got the cursor warped away
mid-gesture, and raw deltas kept streaming to the host while the user fought the window.
Reworked Moonlight-style, with capture as a deliberate, reversible state owned by
StreamLayerView:

- Engage: automatically once when the stream starts / trust is confirmed (one-shot, can
  never fire surprisingly later), or by clicking into the video (that click's
  press/release are suppressed toward the host; acceptsFirstMouse makes it one click
  from another app). NEVER on app re-activation.
- Release: ⌘⎋ (toggles, key-window-scoped), focus loss — now including same-app window
  switches (⌘, / ⌘N / ⌘M resign key without resigning the app; previously the new
  window inherited a hidden frozen cursor and its typing was double-delivered to the
  host) — and disconnect.
- While released: nothing is forwarded (InputCapture.forwarding gates the GC handlers;
  held keys/buttons are flushed host-side so nothing sticks), the cursor is free, and
  the HUD (now showing the capture state) is clickable.
- The no-beep behavior moved from the NSEvent monitor to first-responder key
  consumption — swallowing at the monitor risked starving GC's own delivery (the
  "input broken altogether" report). The monitor now only intercepts ⌘⎋.
- Adversarial-review fixes: a second session preempts the previous one cleanly instead
  of leaving it captured with dead GC handlers (onPreempted); the engage click's
  suppression latch can't outlive the click (mouseUp backstop); ⌘⎋'s physical Esc can't
  type into the host in either toggle direction (suppressedVK latch + Esc-while-⌘
  guard); capture callbacks defer out of the SwiftUI update pass.

Validated live against the box: 16185 input datagrams injected during a captured
session (gamescope EIS), title-bar drag/resize free while released, and visible
cursor + typing on a streamed KWin desktop, all user-confirmed.

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

clients/apple/Sources/PunktfunkClient/SessionModel.swift

@@ -53,9 +53,11 @@ final class SessionModel: ObservableObject {
     @Published var fps = 0
     @Published var mbps = 0.0
     @Published var totalFrames = 0
+    /// Mirrors StreamView's capture state (it owns the input capture; this drives the
+    /// HUD's "click to capture" / "⌘⎋ releases" hint).
+    @Published var mouseCaptured = false
 
     let meter = FrameMeter()
-    private var inputCapture: InputCapture?
     private var statsTimer: Timer?
 
     var isBusy: Bool { phase != .idle }
@@ -118,8 +120,6 @@ final class SessionModel: ObservableObject {
     }
 
     func disconnect() {
-        inputCapture?.stop()
-        inputCapture = nil
         statsTimer?.invalidate()
         statsTimer = nil
         if let conn = connection {
@@ -132,6 +132,7 @@ final class SessionModel: ObservableObject {
         phase = .idle
         fps = 0
         mbps = 0
+        mouseCaptured = false
     }
 
     /// Called (via the main actor) when the pump hits end-of-session.
@@ -143,11 +144,10 @@ final class SessionModel: ObservableObject {
     }
 
     private func beginStreaming() {
-        guard let conn = connection else { return }
+        guard connection != nil else { return }
+        // Input capture itself is owned by StreamView (engaged by the captureEnabled
+        // flip this phase change causes, released/re-engaged by the user from there).
         phase = .streaming
-        let capture = InputCapture(connection: conn)
-        capture.start()
-        inputCapture = capture
     }
 
     private func startStatsTimer() {