Add CI workflow for plugin validation

[EricGrill]

Problem

There's no automated validation to ensure plugins meet the structure and quality standards defined in CONTRIBUTING.md.

Current state:

• No CI workflow validates plugin.json against the schema
• No automated check for required files (LICENSE, README.md)
• Plugin structure varies inconsistently across plugins
• Some plugins don't have .claude-plugin/plugin.json in expected location

Why it matters:
Without automated validation, quality issues accumulate over time. Manual review is error-prone and doesn't scale to 70+ plugins. Standards drift leads to inconsistent user experience.

Suggested Solution

Create a CI workflow that validates:

1. plugin.json exists and is valid JSON
2. plugin.json validates against schemas/plugin-manifest.json
3. Required files present (LICENSE, README.md)
4. Plugin structure follows CONTRIBUTING.md guidelines
5. No secrets or sensitive data in plugin files

Example validation script:

#!/bin/bash
errors=0
for plugin in plugins/*/; do
  if [ ! -f "$plugin/LICENSE" ]; then
    echo "ERROR: $plugin missing LICENSE"
    errors=$((errors+1))
  fi
  if [ ! -f "$plugin/README.md" ]; then
    echo "ERROR: $plugin missing README.md"
    errors=$((errors+1))
  fi
  # Add JSON schema validation
  if [ -f "$plugin/.claude-plugin/plugin.json" ]; then
    npx ajv-cli validate -s schemas/plugin-manifest.json -d "$plugin/.claude-plugin/plugin.json"
  fi
done
exit $errors

Acceptance Criteria

• GitHub Action workflow created for plugin validation
• Validates plugin.json schema compliance
• Validates required files (LICENSE, README.md)
• Runs on every PR affecting plugins/
• Clear error messages for contributors

[EricGrill]

Triage: Roadmap ✅

Decision: Add to Q2 roadmap.
Milestone: v1.0.0 — Repo Foundation
Priority: P1
Automated plugin validation (schema, required files, structure) is critical for scaling to 70+ plugins.