Perf: Optimize macOS screen capture with CGDisplayStream

Core optimization:
- Use CGDisplayStream instead of per-frame CGDisplayCreateImage
- Push model: CPU sleeps when screen is static (condition_variable wait)
- IOSurface capture avoids expensive image creation per frame
- ~47% CPU reduction during active remote desktop (45% → 24%)

Additional optimizations:
- vImageVerticalReflect (SIMD) replaces manual row-by-row flip
- Cache CGColorSpaceRef to avoid per-frame creation/release
- Cache tempBuffer to avoid per-frame memory allocation
- Throttle getCursorTypeIndex to 250ms (Accessibility API is expensive)

Bug fixes:
- Fix unreliable screen capture permission check (use actual capture test)
- Improve permission logging

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

macos/main.mm

@@ -573,6 +573,7 @@ static void signalHandler(int sig)
 {
     NSLog(@"Received signal %d, shutting down...", sig);
     g_running = false;
+    g_bExit = S_CLIENT_EXIT;  // 通知所有工作线程退出
 }
 
 static void setupSignals()
@@ -860,13 +861,25 @@ int main(int argc, const char* argv[])
         // Check permissions
         NSLog(@"Checking permissions...");
 
-        if (!Permissions::checkScreenCapture()) {
+        bool hasScreenCapture = Permissions::checkScreenCapture();
+        if (hasScreenCapture) {
+            NSLog(@"Screen capture permission: OK");
+        } else {
             NSLog(@"Screen capture permission not granted.");
             NSLog(@"Please grant permission in System Preferences > Privacy & Security > Screen Recording");
-            Permissions::openScreenCaptureSettings();
+            // Request permission (triggers system dialog on first run)
+            Permissions::requestScreenCapture();
+            // Only open settings if this appears to be a re-run without permission
+            // Check again after request (dialog may have been shown)
+            if (!Permissions::checkScreenCapture()) {
+                Permissions::openScreenCaptureSettings();
+            }
         }
 
-        if (!Permissions::checkAccessibility()) {
+        bool hasAccessibility = Permissions::checkAccessibility();
+        if (hasAccessibility) {
+            NSLog(@"Accessibility permission: OK");
+        } else {
             NSLog(@"Accessibility permission not granted.");
             NSLog(@"Please grant permission in System Preferences > Privacy & Security > Accessibility");
             Permissions::requestAccessibility();
@@ -877,6 +890,8 @@ int main(int argc, const char* argv[])
             NSLog(@"Full Disk Access: not detected (may be false negative).");
             NSLog(@"If file access issues occur, grant FDA in System Preferences > Privacy & Security > Full Disk Access");
             // Don't auto-open settings since detection is unreliable
+        } else {
+            NSLog(@"Full Disk Access: OK");
         }
 
         // Create client