feat(app): OFX Interact viewer integration - overlay drawing and event forwarding

- Main-process interact instances for the selected OFX effect card
  (create on selection change, describe, destroy on deselect/close),
  coexisting with the render-worker plugin instances per the OFX
  multi-instance model.
- Program viewer composites the interact's overlay: draw into a GL
  FBO via gl_bridge, read back, straight-alpha 'over' composite onto
  the displayed frame; cached and only re-rendered on frame/time/
  viewport/instance change or plugin redraw requests.
- Event forwarding: picture-area pointer maps through the contain-fit
  letterbox inverse to OFX pen coordinates (pen_motion/down/up);
  Keystroke to OFX key symbols (ASCII, navigation, F1-F35) for
  key_down/up; a 50ms idle pump; global shortcut consumption keeps
  precedence.
- e2e with the real test plugin: lifecycle marker assertions, pen/key
  event records, and macOS GL overlay compositing verified (265 tests
  green incl. gpui_widgets viewer suite).

crates/oakplugin/tests/interact_test.rs

@@ -318,8 +318,10 @@ fn interact_draw_renders_plugin_colours() {
 		);
 
 		// 像素断言：矩形区域 (10..30)² 的 GL 像素 → 翻转后 frame y 33..53。
+		// F32 RGBA 每像素 16 字节（紧凑行）。
+		let stride = (w as usize) * 16;
 		let px = |x: usize, y: usize| -> [f32; 4] {
-			let p = &img.pixels()[y * (w as usize) * 4 + x * 4..y * (w as usize) * 4 + x * 4 + 4];
+			let p = &img.pixels()[y * stride + x * 16..y * stride + x * 16 + 16];
 			[
 				f32::from_ne_bytes(p[0..4].try_into().unwrap()),
 				f32::from_ne_bytes(p[4..8].try_into().unwrap()),