loadMintIgnore mis-parses directory patterns without a leading slash

`loadMintIgnore()` handles directory patterns ending in `/*`, but it always removes the first character with `slice(1, -2)`.

File evidence:

- `scripts/lib/docs-utils.js` checks `if (trimmed.endsWith('/*'))`.
- That branch stores `ignored.dirs.add(trimmed.slice(1, -2))`, assuming the pattern starts with `/`.
- The file-pattern branch immediately below supports both leading-slash and bare filenames, so a contributor can reasonably expect `foo/*` to work the same way as `/foo/*`.

For a slashless directory pattern such as `draft-notes/*`, the parser stores `raft-notes`, so the intended directory is not ignored and there is no warning.

Expected behavior: directory patterns should preserve the directory name whether they are written as `/foo/*` or `foo/*`.

Start in scripts/lib/docs-utils.js at loadMintIgnore(), especially the directory-pattern branch that handles paths ending in /*. Check that both /foo/* and foo/* preserve the same directory name, then verify that a slashless pattern such as draft-notes/* is ignored without a warning.

Written by the indexing model from the issue text.