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-romaji.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Fill the Romaji column of 274-dev.md from its Kana column.
+"""Fill the Romaji column of 274-lookup.md from its Kana column.
 
 Kana is the source of truth. Romaji is generated wāpuro-style — no macrons,
 since they are awkward to type: おう→ou, ゅう→yuu, っ doubles the following
@@ -18,7 +18,7 @@ Rows with no kana are left with an empty Romaji cell rather than a guess.
 import io, os, re, sys
 
 HERE = os.path.dirname(os.path.abspath(__file__))
-DOC = os.path.join(HERE, '274-dev.md')
+DOC = os.path.join(HERE, '274-lookup.md')
 
 # stems that must not have a trailing 川 split off — it is part of the name
 NOSPLIT = {'のぼりかわ', 'にいかわ', 'しんかわ', 'みかわ', 'たきさわがわ'}