feat(skills): add 6 generalized AI-driven development skills

- version-bumper: automated multi-file version synchronization
- plugin-scaffolder: standardized 12-language i18n template generation
- doc-mirror-sync: automated README to docs mirroring
- i18n-validator: dictionary key alignment analysis via AST
- gh-issue-replier: professional English reply with star-check logic
- gh-issue-scheduler: unanswered issue audit and action planning

.gemini/skills/gh-issue-replier/references/example_reference.md

@@ -0,0 +1,17 @@
+# Reference Documentation for Gh Issue Replier
+
+This is a placeholder for detailed reference documentation.
+Replace with actual reference content or delete if not needed.
+
+## Structure Suggestions
+
+### API Reference Example
+- Overview
+- Authentication
+- Endpoints with examples
+- Error codes
+
+### Workflow Guide Example
+- Prerequisites
+- Step-by-step instructions
+- Best practices