feat: initial hello-plugin with skill, agent and hook

Plugin de exemplo para Claude Code que demonstra:
- Skill: hello (info do plugin)
- Agent: explorer (explora directorios)
- Hook: PreToolUse log (regista ferramentas usadas)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugin.json

@@ -0,0 +1,27 @@
+{
+  "name": "hello-plugin",
+  "publisher": "descomplicar",
+  "version": "1.0.0",
+  "displayName": "Hello Plugin",
+  "description": "Plugin de exemplo para aprender a estrutura de plugins Claude Code. Inclui skill, agent e hook.",
+  "engines": {
+    "claude-code": ">=1.0.0"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://git.descomplicar.pt/ealmeida/hello-plugin.git"
+  },
+  "components": {
+    "skills": ["./skills/*.md"],
+    "agents": ["./agents/*.md"],
+    "hooks": {
+      "PreToolUse": ["./hooks/log-tools.sh"]
+    }
+  },
+  "keywords": ["example", "tutorial", "hello-world"],
+  "author": {
+    "name": "Emanuel Almeida",
+    "email": "emanuel@descomplicar.pt"
+  }
+}