Volume: quieter/louder buttons that take the remote's own step

Next to the five volume bars, a − and a + button move the volume by
`volume_increment` device units, the same step as the IR remote's volume keys and
the rotary encoder, via a new `{steps}` form of POST /api/volume. The bars still
jump to a percentage.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

python-backend/musicmouse/services/web/api.py

@@ -33,6 +33,7 @@ from musicmouse.events import (
     SetVolumeRequested,
     ToggleScreenRequested,
     UserActivity,
+    VolumeChangeRequested,
 )
 from musicmouse.services.web.hub import StateHub
 from musicmouse.services.web.remote_settings import read_mapping, write_mapping
@@ -212,12 +213,19 @@ def build_router(
     @router.post("/volume", status_code=204)
     def set_volume(body: VolumeIn) -> Response:
         general = app.config.general
+        if body.steps is not None:
+            # The IR remote's own step, in device units - see LircService._handle.
+            return emit(
+                VolumeChangeRequested(delta=general.volume_increment * body.steps, source="web")
+            )
         if body.percent is not None:
             target = body.percent
         elif body.delta_percent is not None:
             target = to_percent(app.player.volume, general) + body.delta_percent
         else:
-            raise HTTPException(status_code=422, detail="percent or delta_percent required")
+            raise HTTPException(
+                status_code=422, detail="percent, delta_percent or steps required"
+            )
         return emit(
             SetVolumeRequested(
                 volume=to_device_volume(max(0, min(100, target)), general), source="web"

python-backend/musicmouse/services/web/schemas.py

@@ -229,10 +229,16 @@ class SeekIn(BaseModel):
 
 
 class VolumeIn(BaseModel):
-    """Either an absolute percentage or a relative step; exactly one of the two."""
+    """An absolute percentage, a relative percentage, or a number of steps; exactly
+    one of the three.
+
+    ``steps`` moves by ``volume_increment`` device units per step - the same step the
+    IR remote's volume keys and the rotary encoder take - rather than by a percentage.
+    """
 
     percent: int | None = Field(default=None, ge=0, le=100)
     delta_percent: int | None = Field(default=None, ge=-100, le=100)
+    steps: int | None = Field(default=None, ge=-10, le=10)
 
 
 class SettingsOut(BaseModel):