Add pre-commit hook support and GitHub Actions CI workflow

Summary

SkillSpector currently has no pre-commit hook definition or GitHub Actions workflow,
making it harder for downstream projects to integrate scanning into their CI pipelines.

Motivation

Many security tools (ruff, semgrep, trivy) ship a .pre-commit-hooks.yaml so
developers can add them to pre-commit with a single config block. SkillSpector's
SARIF output is already CI/CD-ready, but there is no example of how to wire it up.

Proposed solution

1. .pre-commit-hooks.yaml — defines a skillspector hook that runs
   skillspector scan. --no-llm (no API key required). Downstream projects
   pin to a release tag and get automatic skill scanning before every commit.

2. .github/workflows/skillspector.yml — a GitHub Actions workflow that
   scans on push/PR and uploads SARIF results to GitHub Code Scanning so
   Findings appear inline on the PR diff.

3. GitHub community templates — PR template and issue templates so
   contributors follow a consistent format.

4. README update — new "CI/CD Integration" section with copy-paste
   Examples for both integrations.

Start with the proposed files .pre-commit-hooks.yaml and .github/workflows/skillspector.yml, then review the existing skillspector scan . --no-llm command and SARIF output behavior. Add the hook, push/PR workflow, GitHub community templates, and README CI/CD Integration examples, and verify that the documented integrations match the repository's commands and outputs.