fix: surface out_of_range error for unsupported HDMI resolution (>1080p)

[nitishagar]

Problem

When the HDMI source resolution exceeds 1920x1080, the native layer reports real Width/Height but leaves Error empty, so the video state is never classified as out_of_range. The UI then hangs indefinitely on "Loading video stream…" instead of showing the incompatible-resolution error.

Fixes #1482

Change

• Add a small pure helper unsupportedResolutionState in video.go: when Error == "" and Width > 1920 || Height > 1080, set Error = "out_of_range" and Ready = false.
• Apply it in OnVideoStateChange before lastVideoState is stored/emitted, so the existing out_of_range → HDMIErrorOverlay pipeline lights up and rpcGetVideoState reports the same state for automation.

The classification is only applied when no more specific error is already present (no_signal/no_lock still win), and it is idempotent.

Scope

• Go-only, additive: one helper + one call site. No change to the event payload, the UI, or MQTT.
• No frame-rate/interlaced handling and no device-side C detection (possible follow-up).

Testing

• Added TestUnsupportedResolutionState (table-driven): 1920x1080/no-error unchanged; 3840x2160/no-error → out_of_range, Ready=false; existing no_signal/no_lock preserved.
• Device manual check: a >1080p source shows the resolution error overlay instead of an indefinite loading state.