feat(05-02): pinned golden-pair corpus + OSRM-demo fetch tool + populated committed dataset (GREEN)

- routing/test/fixtures/golden-pairs.json: the hand-authored 15-pair pinned
  corpus (D-02/D-12) — origins AND destinations are gazetteer landmarks,
  klBbox + 100 KB gz budget + probe id + alternatives floor pinned
- routing/scripts/fetch-route-fixtures.mjs: the maintainer build tool
  (overpass-topup.mjs pattern) — D-12 boundary in the header, pre-flight
  public-coordinate proof against the gazetteer (1e-4 deg), mandatory
  User-Agent, 1200 ms inter-request delay, one retry on network/5xx,
  collect-then-write, --only=<pairId> single-pair repair merge
- routing/src/data/route-fixtures.json: 15 real OSRM-demo pairs committed
  (1-3 verbatim polyline6 routes each; 8 pairs carry >= 2 alternates),
  ODbL header fields preserved (T-05-06)
- loader-env L3 armed (RED commit 01b0ed6) + C6 re-pinned from the empty-seed
  state to the populated corpus (05-01 documented both as 05-02 handoffs)
- npm delegates: root routing:fixtures; routing fixtures + corpus scripts

routing/package.json

@@ -4,7 +4,9 @@
   "type": "module",
   "scripts": {
     "test": "node test/runner.mjs",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "fixtures": "node scripts/fetch-route-fixtures.mjs",
+    "corpus": "node scripts/route-corpus.mjs"
   },
   "devDependencies": {
     "typescript": "^5.9.3"