docs: drop archived pg-components from sidebar, overview, and website page

[dobby-coder]

Closes #56

Summary

Removes references to the archived pg-components repo from the docs site:

• docs/.vitepress/config.mts — sidebar entry under SDKs
• docs/repos/overview.md — SDKs table row and dependency-graph line
• docs/repos/pg-components.md — entire dedicated page deleted
• docs/repos/postguard-website.md — dropped the @e4a/pg-components mention (verified postguard-website/package.json on main only lists @e4a/pg-js)

Verification

• npm run docs:build — green (5.39s, no broken links to the deleted page)
• grep -rn pg-components docs/ — clean

Reviewer quickstart

```
git fetch origin && git checkout fix/drop-archived-pg-components && npm install && npm run docs:dev
```