Add blog post about media player standby state deprecation (#2726)

Author: emontnemery

blog/2025-07-16-media-player-standby-state-deprecated.md

@@ -0,0 +1,10 @@
+---
+author: Erik Montnemery
+authorURL: https://github.com/emontnemery
+title: "The media player STANDBY state is deprecated"
+---
+
+The media player state `MediaPlayerState.STANDBY` has been deprecated as decided in [home-assistant/architecture#799](https://github.com/home-assistant/architecture/discussions/799) and will be removed in Home Assistant Core 2026.8.
+Integrations should use `MediaPlayerState.IDLE` or `MediaPlayerState.OFF` instead.
+
+For more details, see the [media player developer documentation](/docs/core/entity/media-player#states).