v0.6.0-rc1 — colour temperature, read from the lamp (validation build)

Pre-release for hardware validation. Not for general use.

Everything in the released v0.5.1, plus colour-temperature readback and the
lamp's real Kelvin range (PR 20).

What to check

1. What range does the lamp report?

Download diagnostics and read probe.nodes[].ctl_range. This is the interesting
one. Anything other than ["2700", "6500"] means the mirror shipped in 0.5.1 was
already off-centre on that lamp, and check 3 becomes the one that matters. A
null means the lamp reports no range and the default still stands — also a
valid outcome.

2. Does the temperature now come back from the lamp?

Change the colour temperature from the vendor app (or a wall remote), then
reload the integration. Home Assistant should show what the lamp holds, not
what it last sent. Before this build it could only ever show the latter.

3. Are the colours unchanged?

Set 2700 K and 6500 K, as in the 0.5.1 validation. On a lamp whose reported
range is 2700–6500 these must look exactly as they did. If the reported range is
different, they will shift — and the question becomes whether they are now
right, since they were being mirrored around the wrong midpoint before.

4. Does the slider's range change?

The colour-temperature slider should now offer the lamp's own limits rather than
a fixed 2700–6500.

Check 1 costs one diagnostics download and predicts the rest.