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>

package.json

@@ -38,8 +38,8 @@
     "build:tui": "cd clients/tui && npm run build",
     "build:web": "cd clients/web && npm run build",
     "build:launcher": "cd clients/launcher && npm run build",
-    "ci": "npm run validate && npm run coverage && npm run verify:build-gate && npm run verify:bundle-externals && npm run smoke && npm run smoke:web:firefox && npm run ci:storybook",
-    "ci:storybook": "cd clients/web && npx playwright install chromium && npm run test:storybook",
+    "local:gate": "npm run validate && npm run coverage && npm run verify:build-gate && npm run verify:bundle-externals && npm run smoke && npm run smoke:web:firefox && npm run local:storybook",
+    "local:storybook": "cd clients/web && npx playwright install chromium && npm run test:storybook",
     "verify:build-gate": "node scripts/verify-build-gate.mjs",
     "verify:bundle-externals": "node scripts/verify-bundle-externals.mjs",
     "verify:typecheck-coverage": "node scripts/verify-typecheck-coverage.mjs",