Add RRIM, Multi-Hillshade RGB, and Local Dominance visualizations

Three new visualizations complementing existing SVF/openness/LRM/MSRM:

- RRIM (Red Relief Image Map): RGB composite combining positive openness
  (R), inverted slope (G), negative openness (B). Uses ray-tracing
  to compute both openness values in a single pass.

- Multi-Hillshade RGB: 3 azimuths (315°, 135°, 45°) mapped to R/G/B
  channels with slope blending. Color reveals structure orientation.

- Local Dominance: (dem - local_min) / (local_max - local_min) using
  min/max filters. Measures local height position — complements openness.

Also adds:
- _compute_openness_both() helper for shared ray-tracing (used by RRIM)
- xp_maximum_filter() in gpu.py (GPU/CPU abstraction)
- Entries in COLORMAPS, RGB_LEGENDS, VIZ_STEPS, and is_rgb detection
- All NaN handling follows existing patterns (nan_mask restoration)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lidar_pipeline/rendering.py

@@ -156,6 +156,14 @@ COLORMAPS = {
         'vmin_mode': 'fixed', 'vmin_val': 0,
         'vmax_mode': 'percentile', 'vmax_pct': 98,
     },
+    'local_dominance': {
+        'cmap': 'RdYlBu_r',
+        'title': 'Dominance Locale (position relative dans le voisinage)',
+        'legend': 'Proportion du voisinage sous le point central\nRouge = Point dominant (sommet, crête)\nBleu = Point encaissé (fossé, vallée)\nRayon: 15m',
+        'description': 'Mesure la saillie locale — complémentaire de l\'openness',
+        'vmin_mode': 'percentile', 'vmin_pct': 2,
+        'vmax_mode': 'percentile', 'vmax_pct': 98,
+    },
 }
 
 # RGB entries (ortho/topo) are handled specially
@@ -170,6 +178,16 @@ RGB_LEGENDS = {
         'legend': 'Carte IGN\nPlan topographique',
         'description': 'Carte topographique IGN (Plan IGN)',
     },
+    'rrim': {
+        'title': 'RRIM — Red Relief Image Map (composite RGB)',
+        'legend': 'Rouge = Openness positive (crêtes, levées)\nVert = Pente inversée (plat = clair)\nBleu = Openness négative (fossés, dépressions)',
+        'description': 'Composite RGB synthétique pour prospection archéologique',
+    },
+    'multi_hillshade': {
+        'title': 'Hillshade Composite RGB (3 azimuts)',
+        'legend': 'Rouge = Éclairage NW (315°)\nVert = Éclairage SE (135°)\nBleu = Éclairage NE (45°)',
+        'description': 'Composite couleur révélant les structures selon leur orientation',
+    },
 }
 
 
@@ -282,7 +300,7 @@ def tif_to_png(tif_file, vis_dir, resolution, keep_tif=False, source_info=None):
 
     try:
         with rasterio.open(tif_file) as src:
-            is_rgb = src.count >= 3 and ('ortho' in str(tif_file) or 'topo' in str(tif_file))
+            is_rgb = src.count >= 3 and any(k in str(tif_file) for k in ('ortho', 'topo', 'rrim', 'multi_hillshade'))
 
             if is_rgb:
                 data = src.read([1, 2, 3])