Switch skill CI validation workflows to vally lint (#2030)

* Switch skill CI checks to vally lint

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Adding Vally to allowed words

* case sensitivity

* Migrate external plugin quality gates from skill-validator to vally lint

Replace the downloaded skill-validator binary with
px @microsoft/vally-cli lint
in the external plugin quality gates pipeline:

- Remove downloadSkillValidator() and SKILL_VALIDATOR_ARCHIVE_URL constant
- Replace uildSkillValidatorArgs() + 
unSkillValidatorGate() with
  uildVallyLintArgs() + 
unVallyLintGate() that run
px vally-cli lint
  per resolved skill directory (falling back to the full plugin root when no
  specific skill paths can be resolved from plugin.json)
- Rename result keys skill_validator_status / skill_validator_output
  to ally_lint_status / ally_lint_output throughout both
  ng/external-plugin-quality-gates.mjs and ng/external-plugin-intake.mjs
- Update PR comment markdown to show 'vally lint' instead of 'skill-validator'
- Update CONTRIBUTING.md prose references accordingly

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Use @microsoft/vally library directly instead of vally-cli subprocess

Replace the npx-spawned vally-cli process with a direct call to the
@microsoft/vally core library in the external plugin quality gates scripts:

- Add @microsoft/vally as a devDependency in package.json
- Import runLint and LintConsoleReporter from @microsoft/vally
- Replace runVallyLintGate() process spawn with async API call:
  - runLint({ rootPath }) returns structured LintResults
  - LintConsoleReporter with a Writable capture stream collects
    text output without printing to stdout
- Make runExternalPluginQualityGates() async (propagated to
  runExternalPluginPrQualityGates() and both main entry points)
- Use Promise.all in runExternalPluginPrQualityGates() for parallel
  plugin checks
- Fix remaining skill_validator_status reference in pr-quality-gates
  summary string (now vally-lint=...) and YAML workflow table header
- Add 'npm install @microsoft/vally' step to both calling workflows

This removes a layer of indirection (Node -> npx -> CLI -> library)
and replaces it with a direct in-process library call, which is faster,
more reliable, and gives structured access to lint results.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

package.json

@@ -38,6 +38,7 @@
   "author": "GitHub",
   "license": "MIT",
   "devDependencies": {
+    "@microsoft/vally": "^0.6.0",
     "all-contributors-cli": "^6.26.1"
   },
   "dependencies": {