feat: modern macOS window chrome + Linux build script

macOS:
- Transparent title bar with hidden title, full-size content view
- macOS: inline Row header (no AppBar) with 56px traffic-light pad
- Other platforms: standard Material AppBar unchanged
- App name 'Chanora' in CFBundleName/CFBundleDisplayName (iOS + macOS)
- NSLocalNetworkUsageDescription added to both platforms

Linux:
- tools/build-linux.sh: builds Rust .so + Flutter bundle + tarball
- Verifies GTK3, libopus dev headers, Rust target
- Copies libchanora_bridge.so into bundle/lib/

apps/chanora_flutter/macos/Runner/MainFlutterWindow.swift

@@ -8,8 +8,13 @@ class MainFlutterWindow: NSWindow {
     self.contentViewController = flutterViewController
     self.setFrame(windowFrame, display: true)
 
+    self.titlebarAppearsTransparent = true
+    self.titleVisibility = .hidden
+    self.styleMask.insert(.fullSizeContentView)
+    self.isMovableByWindowBackground = true
+
     RegisterGeneratedPlugins(registry: flutterViewController)
 
     super.awakeFromNib()
   }
-}
+}