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

scripts/build_pattern_zones.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+"""Task 5 (user decision 2026-10-21): no pattern-station data exists. Create a
+PLACEHOLDER pattern table at 2 m segments over the modelled range 4+745..5+480,
+cycling the six pattern names. Every row is marked '임의 배정 (placeholder)'.
+The table is an editable CSV: replace the 'pattern' column later and rebuild.
+Output: data/pattern_zones_placeholder.csv (created only if absent; never overwritten)."""
+import csv
+import os
+import sys
+
+ROOT = sys.argv[1]
+OUT = f"{ROOT}/data/pattern_zones_placeholder.csv"
+PATTERNS = ["NP-4AD-1-D-2", "NP-4BD-1-D-2", "NP-5AE-1-WL-4", "NP-5BE-1-WL-4", "NP-6A", "NP-6B"]
+S0, S1, SEG = 4745, 5480, 2
+if not os.path.exists(OUT):
+    with open(OUT, "w", newline="", encoding="utf-8") as fh:
+        w = csv.writer(fh)
+        w.writerow(["seg_from", "seg_to", "pattern", "status"])
+        for k, s in enumerate(range(S0, S1, SEG)):
+            w.writerow([s, min(s + SEG, S1), PATTERNS[k % len(PATTERNS)], "임의 배정 (placeholder, 실제 구간 아님)"])
+print("pattern table:", OUT)