feat: 2 m placeholder pattern zones on lining, station/pattern readout in viewer (Task 5)

No pattern-to-station data exists in the drawings. Per user decision
(2026-10-21) the modelled range 4+745..5+480 is split into 2 m segments with
arbitrary pattern names, marked placeholder in CSV, meta and viewer, to be
replaced later. Ring step reduced to 1 m so that the 2 m segments align.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A5Cun3RHQKna9qxE6ybZ4A

data/verify_skeleton.json

@@ -5,7 +5,17 @@
   "road_z_4745_m": 50.62,
   "road_z_5480_m": 67.311,
   "plan_chord_length_total_m (4+700..5+500)": 799.905,
-  "station_range_modelled": "4745 .. 5480 (ring step 5.0 m, 148 rings)",
-  "glb_bytes": 470416,
+  "station_range_modelled": "4745 .. 5480 (ring step 1.0 m, 736 rings)",
+  "pattern_zones (2 m, placeholder)": 368,
+  "pattern_coverage_all_stations": true,
+  "pattern_counts": {
+    "NP-4AD-1-D-2": 62,
+    "NP-4BD-1-D-2": 62,
+    "NP-5AE-1-WL-4": 61,
+    "NP-5BE-1-WL-4": 61,
+    "NP-6A": 61,
+    "NP-6B": 61
+  },
+  "glb_bytes": 2201764,
   "glb_reload_geometries": 5
 }