Phase 4: mouse + keyboard input via enigo

- Add enigo 0.6 dependency (x11rb/XTest backend)
- Enigo field in X11Backend for input simulation
- Click, double-click at absolute coords or @wN ref centers
- Type text into focused window, press individual keys
- Hotkey combinations (modifier press, key click, modifier release)
- Mouse move, scroll (vertical/horizontal), drag operations
- parse_key() mapping human-readable names to enigo Key values
- Handler dispatchers with ref resolution and coord parsing

Cargo.toml

@@ -19,3 +19,4 @@ xcap = "0.8"
 image = { version = "0.25", features = ["png"] }
 imageproc = "0.26"
 ab_glyph = "0.2"
+enigo = "0.6"