Update inline strategy.data.gov links in content files

## Summary

Four content files in resources.data.gov contain inline links to `strategy.data.gov/action-plan/`. Update these before the redirect goes live.

## Files and line numbers

| File | Line | Current link |
|------|------|-------------|
| `pages/standards/index.md` | 15 | `https://strategy.data.gov/action-plan/#action-20-develop-a-data-standards-r...` |
| `pages/_keywords/data-standards.md` | 8 | `https://strategy.data.gov/action-plan/#action-20-develop-a-data-standards-r...` |
| `pages/_categories/data-standards.md` | 23 | `https://strategy.data.gov/action-plan/#action-20-develop-a-data-standards-r...` |
| `pages/_resources/dcat-us-priorities.md` | 29 | `https://strategy.data.gov/action-plan/` |

## Task

Update each link to point to one of:
- The archived PDF (if the action plan is being treated as a historical document)
- The relevant section of a migrated resources.data.gov page (if migration is happening per Ticket 1)
- The National Archives URL (if externally archived)

Confirm the target URL in comments based on the Ticket 1 decision.

## Acceptance criteria

- [ ] No remaining inline links to `strategy.data.gov` in resources.data.gov content files
- [ ] All updated links resolve correctly on a preview build

## Depends on

Ticket 1