docs: fix preview port in DOCS_GUIDELINES example

[santhiprakash]

Problem

DOCS_GUIDELINES.md tells doc authors to show npx hyperframes preview output as:

# ✓ Server running at http://localhost:3000
# ✓ Watching for changes...

The CLI default preview port is 3002 (packages/cli/src/commands/preview.ts args.port.default), and the actual startup summary matches packages/cli/README.md (Studio running at http://localhost:3002). Self-sourced docs drift.

Triage / Root cause

The guidelines example predates the current preview default and output format. Sibling docs (packages/cli/README.md, docs/guides/video-editor-cheatsheet.mdx) already use port 3002.

Fix

Update the DOCS_GUIDELINES "Show expected output" example to use port 3002 and the current summary line.

Verification

• python3 ../open-source/scripts/preflight_ship.py --repo heygen-com/hyperframes --local . --branch main --file DOCS_GUIDELINES.md --must-contain 'localhost:3000' --must-not-contain 'localhost:3002' --search 'DOCS_GUIDELINES preview port 3002' → preflight clear
• bun run format:check -- DOCS_GUIDELINES.md → passed
• Commit SSH-signed (gpgsig present on 0e84008da)

Notes / Risks

Docs-only; no behavior change. Sibling to merged #2901/#2902 (studio monorepo port 5190).

[miguel-heygen]

@santhiprakash can you add all the docs incoherences in one pr instead of making multiple prs pls?

[santhiprakash]

Thanks @miguel-heygen — understood. We'll consolidate the docs fixes into this single PR (including the Cursor link updates from #2771) instead of opening more docs-only PRs, then close the duplicate. Going forward we'll batch docs incoherences into one PR for Hyperframes.

[santhiprakash]

@miguel-heygen consolidated here: preview-port fix in DOCS_GUIDELINES.md plus the Cursor link updates from #2771 (docs/guides/skills.mdx, docs/guides/website-to-video.mdx). Closing #2771 as the duplicate — no more separate docs-only PRs from me.

[santhiprakash]

Rebased onto current main (was 336 commits behind / conflicting). Cursor-link edits from #2771 are already obsolete upstream (website-to-video.mdx removed; skills.mdx no longer has those links), so this PR is back to the single DOCS_GUIDELINES preview-port fix. Commit is Verified — CI re-running.