feat(displays): per-display devices + DDC/CI capability entities

Restructure how displays are exposed in Home Assistant:

Each physical monitor is now its own HA device linked to the media-server
hub via `via_device`. The hub keeps the media_player + script buttons; per-
display devices hold the power switch, brightness slider, and the new
capability entities. This lets users place displays in their own area/room
and keeps related entities grouped together in the UI.

New platforms:
- sensor: DisplayResolutionSensor (diagnostic, from EDID)
- binary_sensor: DisplayPrimaryBinarySensor + DisplayPowerControlBinarySensor
  (both diagnostic; help users see why a power switch is or isn't created)
- select: DisplayInputSourceSelect (HDMI1/DP1/...), DisplayColorPresetSelect
  (color temperature), DisplayPictureModeSelect (VCP 0xDC scene modes)
- number: added DisplayContrastNumber alongside brightness

Other changes:
- display_device helper centralises the per-display DeviceInfo; pulls real
  manufacturer/model from EDID; device name no longer prepends the hub
  title since via_device already shows the hierarchy.
- api_client gains set_display_{contrast,input_source,color_preset,picture_mode}
  and stops forcing `?refresh=true` on every poll so HA can ride the
  server's TTL cache instead of triggering full DDC/CI probes per entity.
- select / number entities now check the server's `success` flag and re-
  sync from the actual monitor state when a write was silently rejected
  (some monitors honor reads but ignore writes for certain DDC/CI codes).

Bumps manifest.json to 0.3.0 - the device topology change is user-visible
and existing brightness/power entities migrate to per-display devices on
first reload (unique_ids are preserved).

custom_components/remote_media_player/const.py

@@ -40,6 +40,10 @@ API_BROWSER_PLAY = "/api/browser/play"
 API_DISPLAY_MONITORS = "/api/display/monitors"
 API_DISPLAY_BRIGHTNESS = "/api/display/brightness"
 API_DISPLAY_POWER = "/api/display/power"
+API_DISPLAY_CONTRAST = "/api/display/contrast"
+API_DISPLAY_INPUT_SOURCE = "/api/display/input_source"
+API_DISPLAY_COLOR_PRESET = "/api/display/color_preset"
+API_DISPLAY_PICTURE_MODE = "/api/display/picture_mode"
 
 # Service names
 SERVICE_EXECUTE_SCRIPT = "execute_script"