ci: concise cost-map drift failure + accurate Node comment

- cost-map-sync: use diff -q with an actionable ::error:: message instead of
  dumping the full ~700-line cost map on mismatch.
- publish-npm: drop the specific vitest-4 reference (not on main yet); Node 22 is
  just the current LTS for the JS toolchain.

Author: achris7

.github/workflows/ci.yml

@@ -40,7 +40,11 @@ jobs:
         with:
           persist-credentials: false
       - name: Python and JS cost maps must match
-        run: diff src/floe_guard/cost_map.json js/src/cost_map.json
+        # -q keeps the failure concise (the map is ~700 lines); the message says
+        # what to do rather than dumping the whole diff.
+        run: |
+          diff -q src/floe_guard/cost_map.json js/src/cost_map.json \
+            || { echo "::error::cost_map.json drifted between src/floe_guard/ and js/src/ — re-sync the two copies."; exit 1; }
 
   test:
     runs-on: ubuntu-latest

.github/workflows/publish-npm.yml

@@ -31,7 +31,7 @@ jobs:
 
       - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
-          # Node 22: satisfies the test toolchain (vitest 4 / vite need >=20.19).
+          # Node 22: current LTS, comfortably covers the JS toolchain (Vite/Vitest).
           node-version: '22'
           registry-url: 'https://registry.npmjs.org'