feedback7: asset downloads on a Node that cannot proxy fetch() warn and go direct instead of stopping (follow-up to PR #289)

- With HTTP(S)_PROXY set, Node 22.0–22.20 / 23 cannot route the built-in fetch through it; the port of #289 made
  fetch-assets (and so setup) fail there. Before 0.2.2 those downloads went direct, and a proxy variable left over
  from another tool must not stop a player's first start: restartForEnvProxy now logs the reason and returns false
  (go on in this process), guardDefaultFetch warns once and fetches. A Node that can proxy (≥ 22.21 / ≥ 24) still
  restarts once with NODE_USE_ENV_PROXY=1 and never fetches around the proxy.
- restartForEnvProxy takes an injectable `version` for the test. Tests: assets-env-proxy 9 / 9 (a new case for the
  old-Node path).

tools/fetch-assets.mjs

@@ -19,7 +19,7 @@
 // cheap. Downloads use ~16 parallel connections, 3 retries per direct source,
 // a jsDelivr fallback and an opt-in GitHub proxy (one short attempt per URL).
 // HTTP(S)_PROXY is picked up by restarting once with NODE_USE_ENV_PROXY=1
-// (Node >=22.21 or >=24). An older Node fails instead of fetching directly.
+// (Node >=22.21 or >=24). An older Node warns and fetches directly, as before.
 // Spine atlases get `size:` (and `pma: true` for enemies); every skeleton is
 // parsed to resolve animation roles.
 //