feat(ralph): Add ralph plugin for autonomous PRD implementation

- Add /ralph:prd command for PRD generation with clarifying questions
- Add /ralph:convert command to convert PRD to executable JSON
- Include templates: ralph.sh, prompt.md, prd-template.json
- Include example PRD (prd-hello-api.json)
- Update marketplace.json with ralph plugin v1.0.0
- Update README with ralph documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/ralph/.claude-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "ralph",
+  "description": "Autonomous loop for PRD implementation with Claude Code",
+  "version": "1.0.0",
+  "author": {
+    "name": "Romfast Team"
+  }
+}