ci: skip Go jobs and add docs-site build for docs-only PRs

[bloxster]

Summary

• Add a changes job that queries the GitHub API to detect whether any non-docs/ files changed in the PR
• Go CI jobs (tests, race-tests, lint, bench, kurtosis, repro, sonar, caplin, hive) are skipped when every changed file is under docs/, saving ~30 min of unnecessary CI for docs-only PRs
• Add a docs-site job (npm ci → typecheck → docusaurus build) that runs whenever docs/site/** is touched — onBrokenLinks/onBrokenMarkdownLinks/onBrokenAnchors are all set to throw in the Docusaurus config, so the build catches internal broken links at PR time
• For merge_group and workflow_dispatch the full suite always runs
• changes is included in ci-gate needs — if the gh api call fails the step explicitly errors (exit 1), so the gate fails rather than silently defaulting to skipping jobs
• lint runs for all event types (including merge_group), not just pull_request

CI matrix after this merges

PR type	large-files	docs-site	Go CI
docs/site/** only	✓	✓ build + typecheck	skipped
docs/site/** + code	✓	✓	✓ full suite
code only	✓	skipped	✓ full suite
merge_group	—	✓	✓ full suite

File-pattern logic

A PR is considered docs-only (skips Go CI) when every changed file matches:

^(docs/|llms[^/]*\.txt$|[^/]*\.md$)

i.e. files under docs/, root-level llms*.txt, or root-level *.md. Nested .md files (e.g. execution/README.md) still count as code changes.

Test plan

• This PR itself is not docs-only (changes .github/workflows/) → full Go CI runs, validating the new logic
• Verify changes job outputs code=true for this PR
• After merge, open a docs-only PR and confirm Go jobs are skipped and docs-site runs

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates the CI gate workflow to detect docs-only pull requests and skip expensive Go CI jobs when only docs/** files changed, while adding a dedicated docs-site build (typecheck + Docusaurus build) when docs/site/** is touched.

Changes:

• Add a changes job to classify PRs as “code changed” vs “docs-only”, and conditionally skip Go CI jobs for docs-only PRs.
• Add a reusable docs-site-build.yml workflow and a docs-site job in ci-gate to run npm ci → typecheck → build when docs/site/** changes.
• Wire changes outputs into job if: conditions and include changes/docs-site in the ci-gate aggregation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/docs-site-build.yml	Adds a reusable workflow to typecheck and build the Docusaurus docs site.
.github/workflows/ci-gate.yml	Adds PR-change detection and uses it to skip Go CI for docs-only PRs; triggers docs-site build when needed.

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[bloxster]

Additional fix pushed (llms.txt coverage):

After reviewing #21000, noticed that llms.txt and llms-full.txt live at the repo root (not under docs/), and are regenerated by the Docusaurus build script on every docs update. Without a fix, any PR touching those files would have triggered the full Go CI suite despite being a pure docs change.

Extended the changes job filter pattern from '^docs/' to:
```
'^(docs/|llms[^/].txt$|[^/].md$)'
```

This excludes from the "code changed" check:

• llms[^/]*\.txt$ — root-level llms.txt, llms-full.txt (and any future variants)
• [^/]*\.md$ — root-level *.md files (README.md, CLAUDE.md, etc.)

Nested .md files inside Go packages (e.g. execution/README.md) are still treated as code changes — intentional.