fix(skills): remove phantom resource references and fix CoC links (#447)

Remove references to non-existent resource files (references/, assets/,
scripts/, examples/) from 115 skill SKILL.md files. These sections
pointed to directories and files that were never created, causing
confusion when users install skills.

Also fix broken Code of Conduct links in issue templates to use
absolute GitHub URLs instead of relative paths that 404.

plugins/framework-migration/skills/database-migration/SKILL.md

@@ -401,33 +401,3 @@ module.exports = {
   },
 };
 ```
-
-## Resources
-
-- **references/orm-switching.md**: ORM migration guides
-- **references/schema-migration.md**: Schema transformation patterns
-- **references/data-transformation.md**: Data migration scripts
-- **references/rollback-strategies.md**: Rollback procedures
-- **assets/schema-migration-template.sql**: SQL migration templates
-- **assets/data-migration-script.py**: Data migration utilities
-- **scripts/test-migration.sh**: Migration testing script
-
-## Best Practices
-
-1. **Always Provide Rollback**: Every up() needs a down()
-2. **Test Migrations**: Test on staging first
-3. **Use Transactions**: Atomic migrations when possible
-4. **Backup First**: Always backup before migration
-5. **Small Changes**: Break into small, incremental steps
-6. **Monitor**: Watch for errors during deployment
-7. **Document**: Explain why and how
-8. **Idempotent**: Migrations should be rerunnable
-
-## Common Pitfalls
-
-- Not testing rollback procedures
-- Making breaking changes without downtime strategy
-- Forgetting to handle NULL values
-- Not considering index performance
-- Ignoring foreign key constraints
-- Migrating too much data at once