fix(gui): work_plane 3D view = camera POV + red = excluded points

- Camera at origin (CV frame) looking at +Z with screen-up = CV −Y, so
  the rendered scene matches the camera's vantage point. OrbitControls
  retargets to the plane centroid on fit so rotation feels natural.
- Simplify scatter coloring to two tones: red for filter-excluded points
  (signed_distance < −offset_mm/1000), cyan-white for everything kept.
  Matches the backend filter contract exactly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/index.html

@@ -192,7 +192,7 @@
       <div class="canvas-wrap" style="width:min(100%,720px)">
         <canvas id="wp3dCanvas" width="720" height="360" style="display:block;background:#0a0d11;border:1px solid var(--border);border-radius:4px"></canvas>
       </div>
-      <div class="marker-info">piano viola · verde = inlier · giallo = sopra piano+offset · rosso = sotto piano-offset · grigio = buffer · drag = ruota · wheel = zoom</div>
+      <div class="marker-info">vista camera · piano viola · ciano = punti tenuti · rosso = esclusi (sotto piano−offset) · drag = ruota · wheel = zoom</div>
     </div>
     <div>
       <h2>Calibrazione</h2>