Add tests and multi-platform keybind support (Linux, macOS, Windows)

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

README.md

@@ -34,13 +34,14 @@ Examples: `ctrl+shift+m`, `alt+f9`, `ctrl+alt+delete`
 
 ### Modifiers
 
-| Value   | Key          |
-|---------|--------------|
-| `ctrl`  | Control      |
-| `shift` | Shift        |
-| `alt`   | Alt          |
-| `win`   | Windows key  |
-| `super` | Windows key  |
+| Value   | Windows     | Linux       | macOS       |
+|---------|-------------|-------------|-------------|
+| `ctrl`  | Control     | Control     | Control     |
+| `shift` | Shift       | Shift       | Shift       |
+| `alt`   | Alt         | Alt (Mod1)  | Option      |
+| `win`   | Windows key | Super (Mod4)| Cmd         |
+| `super` | Windows key | Super (Mod4)| Cmd         |
+| `cmd`   | —           | —           | Cmd         |
 
 ### Keys
 
@@ -61,8 +62,23 @@ Examples: `ctrl+shift+m`, `alt+f9`, `ctrl+alt+delete`
 
 ## Build
 
-Cross-compile for Windows from Linux/macOS:
+```bash
+# Windows
+GOOS=windows GOARCH=amd64 go build -ldflags="-s -w" -o discord-lobby-mute.exe .
+
+# Linux
+go build -ldflags="-s -w" -o discord-lobby-mute .
+
+# macOS
+go build -ldflags="-s -w" -o discord-lobby-mute .
+```
+
+> **macOS**: the app needs Accessibility permission to register global hotkeys. Grant it in System Settings → Privacy & Security → Accessibility.
+
+> **Linux**: requires X11 (`libx11-dev`) and CGO enabled.
+
+## Tests
 
 ```bash
-GOOS=windows GOARCH=amd64 go build -ldflags="-s -w" -o discord-lobby-mute.exe .
+go test ./...
 ```