feat: solid model of main line 4+745~5+480 (STEP + GLB), per-pattern selection, viewer rework (Task 8)

- scripts/build_solids.py: B-rep solids from standard section 03-001 (rev2, approved 2026-10-21)
  - lining per 지보패턴 run (independently selectable), excavation band per run
  - road surface (계획고, 280 mm) with per-station superelevation; base/invert ASSUMED
  - side drains (box minus pipe), H/I boxes = 공동구 (assumed); 시설한계 50 mm as reference wires only
  - staged run (4 GB RAM / 180 s per call); STEP and GLB from the same B-rep
- model/tunnel_solids.glb, model/tunnel_solids_meta.json, data/verify_solids.json
- viewer/index.html: solids, pattern and component toggles, click readout, no development text
- STEP (84.6 MB) and model/parts/ are git-ignored; the STEP is generated locally by the script

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

data/verify_solids.json

@@ -0,0 +1,45 @@
+{
+  "solid_count": 128,
+  "runs": 40,
+  "pattern_coverage": "4745..5480 contiguous",
+  "lining_runs": 40,
+  "excavation_runs": 40,
+  "volume_sum_m3": 12406.136,
+  "step_bytes": 84621457,
+  "glb_bytes": 1287912,
+  "glb_geometries": 134,
+  "section_overlap_m2_by_station": {
+    "4745": {
+      "lining_vs_excavation": 0.01732111,
+      "base_vs_pavement": 0.0,
+      "lining_vs_base": 0.0,
+      "pavement_vs_lining": 0.0,
+      "base_vs_drainL": 0.0,
+      "base_vs_drainR": 0.0
+    },
+    "5105": {
+      "lining_vs_excavation": 0.01732111,
+      "base_vs_pavement": 0.0,
+      "lining_vs_base": 0.0,
+      "pavement_vs_lining": 0.0,
+      "base_vs_drainL": 0.0,
+      "base_vs_drainR": 0.0
+    },
+    "5165": {
+      "lining_vs_excavation": 0.01732111,
+      "base_vs_pavement": 0.0,
+      "lining_vs_base": 0.0,
+      "pavement_vs_lining": 0.0,
+      "base_vs_drainL": 0.0,
+      "base_vs_drainR": 0.0
+    },
+    "5480": {
+      "lining_vs_excavation": 0.01732111,
+      "base_vs_pavement": 0.0,
+      "lining_vs_base": 0.0,
+      "pavement_vs_lining": 0.0,
+      "base_vs_drainL": 0.0,
+      "base_vs_drainR": 0.0
+    }
+  }
+}