v1.0.1.86 — hotfix: neon artifacts in low-light shots

Hotfix for the v1.0.1.85 field report: bright neon artifacts across low-light pictures. Two mechanisms, both fixed:

1. Chroma-speckle amplification — the low-light lift scaled all channels by the per-pixel gain (up to 4–6× in deep shadows), turning dark chroma noise into saturated confetti. The lift now decomposes each pixel around its luma: luma gets the full lift, chroma is capped at 1.5×. Real-capture A/B: neon pixels 6.61% → 0.09% of the worst dark frame; strong colors at moderate lifts unchanged.
2. AWB-wedge whole-frame casts — some cameras intermittently ship frames with white balance effectively unapplied (a uniform green cast, the sibling of the known magenta wedge; pre-existing, previously hidden because low-light output stayed dark). These frames are now detected (uniform ±60 DN cast on both channels — no real scene is that uniform) and rendered as clean monochrome instead of glowing neon (real-capture proof: solid green rg=−136 → neutral +2).

The low-light improvements themselves are unchanged: edge-preserving noise reduction, hybrid brightness lift (dark shots reach the target instead of staying at ~half), and the dark-scene 8× analog gain ceiling.

New regression tests: 10 host tests including a neon guard that fails on the v1.0.1.85 code, plus a color-validation rule for all future pixel-pipeline changes. Camera (S3) firmware unchanged from v1.0.1.85 — no camera reflash on boot.