feat: 实现 4 个 NAPI 包 — modifiers/image-processor/audio-capture/url-handler

- modifiers-napi: 使用 Bun FFI 调用 macOS CGEventSourceFlagsState 检测修饰键
- image-processor-napi: 集成 sharp 库，macOS 剪贴板图像读取 (osascript)
- audio-capture-napi: 基于 SoX/arecord 的跨平台音频录制
- url-handler-napi: 完善函数签名（保持 null fallback）
- 修复 image-processor 类型兼容性问题

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/modifiers-napi/src/index.ts

@@ -1,5 +1,68 @@
-export function prewarm(): void {}
+import { dlopen, FFIType, suffix } from "bun:ffi";
 
-export function isModifierPressed(_modifier: string): boolean {
-  return false
+const FLAG_SHIFT = 0x20000;
+const FLAG_CONTROL = 0x40000;
+const FLAG_OPTION = 0x80000;
+const FLAG_COMMAND = 0x100000;
+
+const modifierFlags: Record<string, number> = {
+  shift: FLAG_SHIFT,
+  control: FLAG_CONTROL,
+  option: FLAG_OPTION,
+  command: FLAG_COMMAND,
+};
+
+// kCGEventSourceStateCombinedSessionState = 0
+const kCGEventSourceStateCombinedSessionState = 0;
+
+let cgEventSourceFlagsState: ((stateID: number) => number) | null = null;
+
+function loadFFI(): void {
+  if (cgEventSourceFlagsState !== null || process.platform !== "darwin") {
+    return;
+  }
+
+  try {
+    const lib = dlopen(
+      `/System/Library/Frameworks/Carbon.framework/Carbon`,
+      {
+        CGEventSourceFlagsState: {
+          args: [FFIType.i32],
+          returns: FFIType.u64,
+        },
+      }
+    );
+    cgEventSourceFlagsState = (stateID: number): number => {
+      return Number(lib.symbols.CGEventSourceFlagsState(stateID));
+    };
+  } catch {
+    // If loading fails, keep the function null so isModifierPressed returns false
+    cgEventSourceFlagsState = null;
+  }
+}
+
+export function prewarm(): void {
+  loadFFI();
+}
+
+export function isModifierPressed(modifier: string): boolean {
+  if (process.platform !== "darwin") {
+    return false;
+  }
+
+  loadFFI();
+
+  if (cgEventSourceFlagsState === null) {
+    return false;
+  }
+
+  const flag = modifierFlags[modifier];
+  if (flag === undefined) {
+    return false;
+  }
+
+  const currentFlags = cgEventSourceFlagsState(
+    kCGEventSourceStateCombinedSessionState
+  );
+  return (currentFlags & flag) !== 0;
 }