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.