Fix #17: Convert requirements-clarity to correct plugin directory format

- Restructured from .claude/plugins/ to requirements-clarity/.claude-plugin/
- Plugin metadata in marketplace.json (not claude.json)
- Commands in requirements-clarity/commands/clarif.md
- Agent in requirements-clarity/agents/clarif-agent.md
- All prompts in English
- Updated root .claude-plugin/marketplace.json to register plugin
- Removed duplicate files from development-essentials
- Removed old .claude/plugins/requirements-clarity directory

Plugin now follows correct Claude Code plugin directory structure.

Generated by swe-agent

.claude-plugin/marketplace.json

@@ -149,6 +149,35 @@
       "agents": [
         "./agents/gpt5.md"
       ]
+    },
+    {
+      "name": "requirements-clarity",
+      "source": "./requirements-clarity/",
+      "description": "Transforms vague requirements into actionable PRDs through systematic clarification with 100-point scoring system",
+      "version": "1.0.0",
+      "author": {
+        "name": "Claude Code Dev Workflows",
+        "url": "https://github.com/cexll/myclaude"
+      },
+      "homepage": "https://github.com/cexll/myclaude",
+      "repository": "https://github.com/cexll/myclaude",
+      "license": "MIT",
+      "keywords": [
+        "requirements",
+        "clarification",
+        "prd",
+        "specifications",
+        "quality-gates",
+        "requirements-engineering"
+      ],
+      "category": "essentials",
+      "strict": false,
+      "commands": [
+        "./commands/clarif.md"
+      ],
+      "agents": [
+        "./agents/clarif-agent.md"
+      ]
     }
   ]
 }