chore(scripts): rename the local pre-push gate off ci, and guard it out of CI (#2146)

The root `ci` script was never what runs in GitHub CI, and the name worked
against us three ways: it collides with the built-in `npm ci` (which does
something else entirely and is one keystroke away), it invites the
cross-engine passes into a workflow by looking like the thing a workflow
should call, and it blurs "GitHub CI" and "the local gate" in every doc
that names it.

- Rename `ci` → `local:gate` and `ci:storybook` → `local:storybook`, with
  no back-compat alias: `npm run ci` now fails with npm's missing-script
  error, which prints the available scripts.

- Add `scripts/lib/workflow-gate.mjs` + its `test:scripts` suite, which
  runs over the repo's real `.github/workflows/**` and fails on an
  invocation of a `local:*` script, of a non-Chromium engine pass (derived
  from SUPPORTED_BROWSERS), or of `smoke:web:engine`, or on `SMOKE_BROWSER`
  set to anything but a literal `chromium`. It does not forbid
  `npm run smoke`, `smoke:web:chromium` or `smoke:tui` — those belong in CI
  and are there today. Comments are not scanned, so the workflow can still
  explain itself. This is the durable half; the rest is prose.

- Document the two-tier model once, in the root README ("Two tiers: GitHub
  CI and the local gate"), and point the other docs at it rather than
  restating the split.

- Sweep the ~40 stale references across README, AGENTS.md,
  .github/copilot-instructions.md, the client READMEs, the roadmap doc and
  the script headers. AGENTS.md and copilot-instructions.md change
  together, per the mirror rule.

No gate changes what it actually runs.

Signed-off-by: Cliff Hall <cliff@futurescale.com>
Signed-off-by: cliffhall <cliff@futurescale.com>

.github/workflows/main.yml

@@ -88,6 +88,14 @@ jobs:
         run: npx playwright install --with-deps chromium
 
       - name: Run cross-client smokes
+        # NOTE: this workflow runs GitHub CI's tier only. The LOCAL pre-push
+        # gate is `npm run local:gate`, and it is a strict superset — do not add
+        # it, a `local:*` script, `smoke:web:firefox`/`smoke:web:webkit`,
+        # `smoke:web:engine`, or a non-Chromium `SMOKE_BROWSER` to any workflow.
+        # `npm run test:scripts` fails if you do (scripts/lib/workflow-gate.mjs,
+        # #2146). `npm run smoke` and `smoke:web:chromium` belong here and are
+        # not affected. The canonical CI-vs-local table is in the root README.
+        #
         # End-to-end smokes through the built launcher (--help dispatch + prod
         # CLI/web). Not part of any client's `validate`: it needs the
         # cli/tui/launcher bundles, which `validate` above already built