CI: parse every web-dashboard JavaScript module with node --check

[erikdarlingdata]

Fixes #4672.

What's added

• .github/scripts/check-web-js.sh [root]: finds every *.js under Darling/PerformanceMonitor.Darling.Service/wwwroot/js, copies each to a temp .mjs (so Node parses it as an ES module whatever the nearest package.json says), runs node --check, prints OK <file> or FAIL <file> with Node's error, and exits non-zero if any file fails (or none is found). Runs locally the same way. shellcheck clean.
• web-js-syntax job ("Web dashboard JS syntax") at the end of build.yml, on ubuntu-latest with its preinstalled Node (no setup-node action to pin). Only existing action pins used: actions/checkout@v7, dorny/paths-filter@v4.
• The job has no needs:, so it does not depend on the build job. It always reports a result, so it can be a required check. Branch protection must list "Web dashboard JS syntax" for it to gate merges.

Docs fast path

The job is independent of the build job's classify step. On a PR, a webjs filter (wwwroot/js/**, the script, build.yml) decides whether the parse step runs. A docs-only PR leaves it false, so the parse is skipped, a notice is printed, and the job goes green after a checkout. Push, release and merge_group runs always parse (about a second).

Verified

• RED on 7638ce0's app.js (copied into a temp tree): FAIL .../js/app.js ... Illegal return statement, 23 file(s) checked, 1 failed, exit 1.
• GREEN on dev's tree: 23 file(s) checked, 0 failed, every file OK.
• Capability checks: duplicate top-level function f(){} gives SyntaxError: Identifier 'f' has already been declared; top-level return 1; gives SyntaxError: Illegal return statement.
• DarlingPathFilterGateTests, LockedModeRestoreCoverageTests, CiClusterWorkerSizingTests, NightlyVersionInjectionTests (build.yml readers) pass locally. The workflow itself is only exercised by CI.

Notes

Release-notes line for a "CI" note: CI now parses and links every web-dashboard JavaScript module inside the build job, and fails the build on a syntax error, a missing file or a missing export (#4672).

CI proof: the gate has gone red once, and green on both sides of it

The check is a step inside build ("Parse and link every wwwroot/js module"), so a failure fails build itself.

1. The step runs (0b9387351, build success): https://github.com/erikdarlingdata/PerformanceMonitor/actions/runs/36493882293. Pass 1: 23 file(s) checked, 0 failed. Pass 2: linked 23 modules, 0 failure(s).
2. The step fails the build (0c400fc2a, a deliberate export const ciProofDeliberateSyntaxError = ; in derive.js, build FAILURE on this step): https://github.com/erikdarlingdata/PerformanceMonitor/actions/runs/36494925388. Pass 1: FAIL …/wwwroot/js/derive.js, 23 file(s) checked, 1 failed. Pass 2: linked 22 modules, 5 failure(s) (derive.js, plus the modules that import it).
3. The revert is green (7e549f435, a normal git revert; the tree is identical to 0b9387351, build success): https://github.com/erikdarlingdata/PerformanceMonitor/actions/runs/36495420375. Pass 1: 23 file(s) checked, 0 failed. Pass 2: linked 23 modules, 0 failure(s).

The squash merge removes the two proof commits from dev's history; the tree is unchanged by them.

CHANGELOG

None: CI-only change (a build-job step that parses and links the web-dashboard JavaScript).