ptt: change default key from space to f4

Space conflicts with chat input. F4 is unused by default
in most terminal emulators and won't interfere with typing.

docs/USAGE.md

@@ -12,7 +12,7 @@ tuimble --host mumble.example.com --user myname
 | Key | Action |
 |-----|--------|
 | `q` | Quit |
-| `space` | Push-to-talk (configurable) |
+| `F4` | Push-to-talk (configurable) |
 | `Enter` | Send message |
 | `Ctrl+C` | Quit |
 

src/tuimble/config.py

@@ -28,7 +28,7 @@ class AudioConfig:
 
 @dataclass
 class PttConfig:
-    key: str = "space"
+    key: str = "f4"
     mode: str = "hold"  # hold | toggle
     backend: str = "auto"  # auto | kitty | evdev | toggle
 

tests/test_config.py

@@ -19,5 +19,5 @@ def test_server_config():
 
 def test_ptt_config_defaults():
     ptt = PttConfig()
-    assert ptt.key == "space"
+    assert ptt.key == "f4"
     assert ptt.backend == "auto"