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/templates/prd-template.json

@@ -0,0 +1,19 @@
+{
+  "projectName": "feature-name",
+  "branchName": "ralph/feature-name",
+  "description": "Descriere scurtă a feature-ului",
+  "userStories": [
+    {
+      "id": "US-001",
+      "title": "Titlu story",
+      "description": "As a [user type], I want [feature] so that [benefit]",
+      "priority": 1,
+      "acceptanceCriteria": [
+        "Criteriu specific și verificabil",
+        "npm run typecheck passes"
+      ],
+      "passes": false,
+      "notes": ""
+    }
+  ]
+}