feat(audio,macos): live IOHIDCheckAccess for Input Monitoring permission

Replaces the macOS PTT backend's query_permission() stub (which had
returned Undetermined unconditionally) with a real IOKit call:

  extern "C" { fn IOHIDCheckAccess(request_type: u32) -> u32; }
  IOHIDCheckAccess(kIOHIDRequestTypeListenEvent = 1)

Returns Granted (0), Denied (1), or Unknown (2). The existing 1.5 s
re-query worker now drives real descriptor transitions when the user
grants or revokes Input Monitoring in System Settings: the watch
sender republishes the descriptor, ChanoraSession forwards
BridgeEvent::PttCapability, and the Flutter capability badge updates
within ~1.5 s without an app restart.

Verified live on the M1 Mac:
  rustc /tmp/check_perm.rs && ./check_perm
  IOHIDCheckAccess(ListenEvent) = 2 (Unknown)
This is the expected initial state on a fresh box where Chanora has
not yet attempted CGEventTapCreate; once the next commit lands the
event-tap worker, the macOS Input Monitoring prompt will fire on
first audio start and the value transitions to Granted/Denied.

Tests: chanora_audio 28 / 0 / 0 on macOS (Linux had 32; the 4-test
delta is the Linux-only portal probe tests). The existing 7 macOS
backend unit tests still cover the descriptor builder + state
machine purely; they don't exercise the live IOKit call (which
would need a TCC-aware test harness).

SDD-085 reference: macOS Event Tap backend / L2 / L3 capability;
SRS-198 honest capability advertising.

crates/chanora_audio/src/ptt_backends/macos.rs

@@ -58,15 +58,31 @@ impl PermissionState {
 }
 
 fn query_permission() -> PermissionState {
-    // Live `IOHIDCheckAccess` query lands in the macOS platform
-    // verification commit (it needs the IOKit framework link).
-    // Until then we report `Undetermined` so the descriptor stays
-    // at `L0Focused` and the audio engine continues with the
-    // Focused widget — honest reporting, no over-claim. The
-    // periodic re-query loop below still exercises the watch
-    // sender path so a future replacement of this function
-    // automatically engages the runtime upgrade.
-    PermissionState::Undetermined
+    // Live IOHIDCheckAccess query against the IOKit HID subsystem.
+    // The Input Monitoring permission ("Listen Event" access type)
+    // is what gates CGEventTap from receiving global key/mouse
+    // events. Returns the live permission state every call; the
+    // periodic re-query loop in `MacOSEventTapBackend::start`
+    // republishes the descriptor whenever this value transitions.
+    //
+    // SAFETY: IOHIDCheckAccess is a thread-safe synchronous IOKit
+    // entry point with no side effects beyond reading a system
+    // preference. The `#[link]` attribute on the extern block
+    // resolves at build time against the IOKit framework. The u32
+    // return value maps directly onto the documented
+    // IOHIDAccessType enumerator { Granted=0, Denied=1, Unknown=2 }.
+    #[link(name = "IOKit", kind = "framework")]
+    extern "C" {
+        fn IOHIDCheckAccess(request_type: u32) -> u32;
+    }
+    // kIOHIDRequestTypeListenEvent == 1 per IOHIDLib.h.
+    const REQUEST_TYPE_LISTEN_EVENT: u32 = 1;
+    let raw = unsafe { IOHIDCheckAccess(REQUEST_TYPE_LISTEN_EVENT) };
+    match raw {
+        0 => PermissionState::Granted,
+        1 => PermissionState::Denied,
+        _ => PermissionState::Undetermined,
+    }
 }
 
 /// Try to construct the macOS event-tap backend. Returns `None`