[lumina] Validate lumina.encoding.pq.m is positive

[jackylee-ch]

Purpose

capPqM's Javadoc requires pq.m to be > 0 && <= dimension; the body checked only the upper bound, so lumina.encoding.pq.m = 0 reached the native trainer instead of failing here. Javadoc and clamp both arrived in 410e1267b (#7330), so the two bounds were never deliberately different — the upper one keeps clamping because tightening it would break tables that build today.

Open question

If the native trainer reads pq.m = 0 as "auto", such indexes exist, and since toLuminaOptions() is also on the read path (LuminaVectorGlobalIndexReader:253, :377) this would fail their searches too. lumina-jni is external; can anyone confirm?

Tests

LuminaVectorOptionsTest#testEncodingPqMBounds (capPqM had no coverage). Reverting the fix:

Expecting code to raise a throwable.

Written with Claude Code; verification is mine.