fix: schema description for file type

[3096]

Checklist

• make test-all (UNIX) passes. CI will also test this
• unit and/or integration tests are included (not applicable: schema-only change, no code path altered)
• documentation is changed or added (schema description updated)

Description of change

This PR updates docs/schema.yaml so that the fileTest.filetype enum fully reflects all file types that the runtime (system/file.go) can return. Previously, the schema only listed file, symlink, and directory. It now includes:

• file
• symlink
• directory
• socket
• character-device
• block-device
• pipe

Additionally, the description of the file resource was expanded to enumerate these types.

Motivation:
Tools (IDEs, schema validators, autocomplete) relying on docs/schema.yaml were unaware of valid values like socket, causing false validation errors and poorer authoring experience. Aligning the schema with the runtime improves correctness and usability.

Evidence:
Supported types are returned by DefFile.Filetype() in system/file.go:

	switch {
	case fi.Mode()&os.ModeSymlink == os.ModeSymlink:
		return "symlink", nil
	case fi.Mode()&os.ModeDevice == os.ModeDevice:
		if fi.Mode()&os.ModeCharDevice == os.ModeCharDevice {
			return "character-device", nil
		}
		return "block-device", nil
	case fi.Mode()&os.ModeNamedPipe == os.ModeNamedPipe:
		return "pipe", nil
	case fi.Mode()&os.ModeSocket == os.ModeSocket:
		return "socket", nil
	case fi.IsDir():
		return "directory", nil
	case fi.Mode().IsRegular():
		return "file", nil
	}

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📚 Documentation preview 📚: https://goss--1041.org.readthedocs.build/en/1041/