Scope ALSA get_state() to Playback channels on mixed Capture/Playback controls (#237)

`AlsaVolumeController.get_state()` could parse the wrong value on mixer
elements that expose both Capture and Playback channels, because `amixer
sget` output was not constrained to Playback. This change makes
`get_state()` explicitly read Playback state and locks that behavior
with focused tests.

- **Playback-only ALSA state read**
  - Updated `get_state()` to call:
    - `amixer -M -c <card> sget <element> playback`
- This aligns read-path behavior with `set_state()` (already using
`playback`) and avoids capture-line ambiguity in mixed controls.

- **Regression coverage for mixed-channel elements**
- Added a targeted test asserting `get_state()` invokes `sget ...
playback`.
- Updated existing command expectation in ALSA controller tests to
include the playback qualifier.

```python
proc = await asyncio.create_subprocess_exec(
    "amixer",
    "-M",
    "-c",
    self._card,
    "sget",
    self._element,
    "playback",
    stdout=asyncio.subprocess.PIPE,
    stderr=asyncio.subprocess.PIPE,
)
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: balloob <1444314+balloob@users.noreply.github.com>

Author: Copilot

sendspin/alsa_volume.py

@@ -205,6 +205,7 @@ async def get_state(self) -> tuple[int, bool]:
             self._card,
             "sget",
             self._element,
+            "playback",
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE,
         )

tests/test_alsa_volume.py

@@ -271,6 +271,30 @@ async def test_get_state_mono_channel(monkeypatch) -> None:
     assert muted is False
 
 
+async def test_get_state_requests_playback_only(monkeypatch) -> None:
+    """get_state scopes amixer query to playback channels."""
+    calls: list[tuple[str, ...]] = []
+    amixer_output = (
+        "Simple mixer control 'Headset',0\n"
+        "  Capabilities: pvolume pswitch cvolume cswitch\n"
+        "  Playback channels: Front Left - Front Right\n"
+        "  Capture channels: Front Left - Front Right\n"
+        "  Front Left: Playback 20 [80%] [on]\n"
+        "  Front Right: Playback 20 [80%] [on]\n"
+    )
+
+    async def fake_exec(*argv: object, **kwargs: object) -> _FakeProcess:
+        calls.append(argv)
+        return _FakeProcess(stdout=amixer_output.encode())
+
+    monkeypatch.setattr(asyncio, "create_subprocess_exec", fake_exec)
+    ctrl = AlsaVolumeController(card=0, element="Headset")
+    volume, muted = await ctrl.get_state()
+    assert calls == [("amixer", "-M", "-c", "0", "sget", "Headset", "playback")]
+    assert volume == 80
+    assert muted is False
+
+
 # -- AlsaVolumeController.start_monitoring ------------------------------------
 
 
@@ -422,7 +446,7 @@ async def fake_exec(*argv: object, **kwargs: object) -> _FakeProcess:
 
     # Read back the volume
     volume, muted = await ctrl.get_state()
-    assert calls[-1] == ("amixer", "-M", "-c", "1", "sget", "Digital")
+    assert calls[-1] == ("amixer", "-M", "-c", "1", "sget", "Digital", "playback")
     assert volume == 74
     assert muted is False