274: rename the roster to 274-lookup.md, method notes to 274-dev.md

The file called 274-dev.md was never dev notes — it was the roster. It
now sits alongside 274-lookup.csv and 274-lookup.geojson under the same
stem, since all three carry the same table.

  274-dev.md    -> 274-lookup.md   the roster, source of truth
  274-method.md -> 274-dev.md      how it was built

References updated: DOC in 274-romaji.py, the roster path in
274-transect-build.py, and the docstrings in both. 274.md now links to
the dev notes and the reference tables separately; each of the two docs
links to the other and back to the song page.

Titles follow: "274 - reference tables" and "274 - how the roster was
built".

Verified after renaming: 274-romaji.py --check reports no changes and
274-transect-build.py rebuilds 168 entries, so neither script lost its
input.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S6MpcBisZYhX45oDGRRJoz

wip/274-transect-build.py

@@ -1,14 +1,14 @@
 #!/usr/bin/env python3
-"""Rebuild the data payload inside 274-transect.html from 274-dev.md.
+"""Rebuild the data payload inside 274-transect.html from 274-lookup.md.
 
 The HTML is self-contained: it carries its data in a <script id="data"> block so
 it opens straight from disk. This script re-reads the roster table out of
-274-dev.md, joins the route line and district bands, and writes the payload back
+274-lookup.md, joins the route line and district bands, and writes the payload back
 into the HTML in place. The page's markup, CSS and JS are left untouched.
 
     python3 274-transect-build.py
 
-Inputs : 274-dev.md (roster, source of truth), 274-route.json, 274-districts.json
+Inputs : 274-lookup.md (roster, source of truth), 274-route.json, 274-districts.json
 Output : 274-transect.html (data block replaced)
 """
 import io, json, os, re, sys
@@ -48,7 +48,7 @@ def main():
     cities = sorted({b['city'] for b in bands if b.get('city')}, key=len, reverse=True)
 
     items = []
-    for r in roster(p('274-dev.md')):
+    for r in roster(p('274-lookup.md')):
         items.append(dict(
             km=float(r['km']), name=r['Name'], obj=r['Object'],
             kana=r.get('Kana', ''), romaji=r.get('Romaji', ''), kind=r['Kind'],