chore: add root self-validation skill

Author: moonrunnerkc

CHANGELOG.md

@@ -33,6 +33,7 @@ Backward compatibility: previously-passing skills still pass. Some previously-fa
 - Renamed `config.KNOWN_FRONTMATTER_FIELDS` to `config.SPEC_FIELDS`.
 - New `template.detected` rule wired into `rules/__init__.py`.
 - Frontmatter rule implementation split into smaller modules while preserving `skillcheck.rules.frontmatter` imports.
+- Root `SKILL.md` restored so `skillcheck SKILL.md` self-validation works from the repository root.
 - New fixture set under `tests/fixtures/` covering ecosystem fields, user extensions, template detection, and demoted severities.
 
 ## [1.1.0] - 2026-04-28

SKILL.md

@@ -0,0 +1,44 @@
+---
+name: skillcheck
+description: Validates SKILL.md files for spec-facing structure, sizing, references, cross-agent compatibility, and agent-authored critique or graph diagnostics.
+version: "1.2.0"
+author: brad
+---
+
+Use this skill when validating a `SKILL.md` file or a directory of skill files with the `skillcheck` CLI.
+
+## Validate
+
+Run the default symbolic checks:
+
+```bash
+skillcheck SKILL.md
+skillcheck skills/ --format json
+```
+
+The report includes errors, warnings, and info diagnostics. Exit code 0 means no errors. Exit code 1 means at least one error, or warnings with `--warnings-as-errors`. Exit code 2 means input or argument error. Exit code 3 means symbolic validation passed but ingested agent critique found semantic errors.
+
+## Agent workflows
+
+For semantic self-critique, emit a prompt and ingest the returned JSON:
+
+```bash
+skillcheck SKILL.md --emit-critique-prompt > prompt.txt
+skillcheck SKILL.md --ingest-critique response.json
+```
+
+For capability graph work, use:
+
+```bash
+skillcheck SKILL.md --analyze-graph
+skillcheck SKILL.md --emit-graph --format json
+```
+
+## Configuration
+
+`skillcheck.toml` can set CLI defaults and frontmatter extension fields:
+
+```toml
+[frontmatter]
+extension_fields = ["my-org-tag", "internal-id"]
+```