queryCollection by path prefix

Is your feature request related to a problem? Please describe

We usually place relevant file in different directory:

• getting-started/
  • index.md
  • introduction.md
  • installation.md
  • ...

Sometime we may want to query all page under a directory, but

const { data } = await useAsyncData("/getting-started/", () =>
  queryCollection("content").path("/getting-started/").all(),
);

won't work, as `.path()" is exact match, not prefix match.

Describe the solution you'd like

const { data } = await useAsyncData("/getting-started/", () =>
  queryCollection("content").path("/getting-started/").all(),
);

• With trailing slash (/getting-started/) means query all page under directory
• Without trailing slash (/getting-started) means query a file (getting-started.md) or an index file (getting-started/index.md).

Describe alternatives you've considered

.where("path", "LIKE", "/getting-started/%")

Additional context

Start at the queryCollection().path() API described in the issue and inspect its existing exact-path behavior. Add coverage for trailing-slash directory prefixes and non-trailing-slash file or index lookups, then run the relevant query-collection tests to confirm both forms work.