[Broken Link] Fix internal broken links in DCAT-US schema pages

## What needs to change
Several pages within the DCAT-US schema documentation contain internal links to resources.data.gov/dcat-us/ and related anchor URLs that all return 404. These are links within the site pointing to other pages on the same site that no longer exist at those paths.

## Where to find them
The confirmed affected files from the link checker report (issue #811) are:
- `pages/_resources/dcat-us.md`
- `pages/_resources/dcat-us-priorities.md`
- `pages/_resources/inventory-data-gov-guide.md`
- `pages/_resources/documenting-apis.md`
- `pages/_resources/podm-field-mapping.md`

## What the broken links look like
Links in these files reference paths like:
- `https://resources.data.gov/dcat-us/`
- `https://resources.data.gov/dcat-us/#contactPoint`
- `https://resources.data.gov/dcat-us/#dataQuality`
- `https://resources.data.gov/dcat-us/#keyword`
- `https://resources.data.gov/dcat-us/#references`
- `https://resources.data.gov/documenting-apis/`
- `https://resources.data.gov/m-13-13-guidance/`
- `https://resources.data.gov/podm-field-mapping/`

## What to do
First, determine whether these destination pages exist at a different path. Check the following:
1. Visit https://resources.data.gov/resources/dcat-us/ — if it resolves, the links just need the `/resources/` prefix added
2. Check `pages/_resources/` in the repo to confirm whether `dcat-us.md`, `documenting-apis.md`, `m-13-13-guidance.md`, and `podm-field-mapping.md` exist as files

If the destination files exist but at a different URL path, update all internal links to match the correct path. If the destination files do not exist, remove the broken links from the source files.

## How to verify
Visit each of the five affected pages on the live site and click every internal link. Confirm none return 404.