fix(marketplace): align manifest with claude-code schema

Remove invalid top-level homepage/repository/license fields.
Move repository to plugin entry as string per schema spec.
Add $schema reference for editor validation.

.claude-plugin/marketplace.json

@@ -1,4 +1,5 @@
 {
+  "$schema": "https://json.schemastore.org/claude-code-marketplace.json",
   "name": "idea2self-ecosystem",
   "description": "Idea2Self — Von vager Idee zu messbarem nächsten Schritt. Sammlung von Claude-Code-Plugins rund um Ideenentwicklung, Validierung und Umsetzung.",
   "owner": {
@@ -6,12 +7,6 @@
     "email": "kontakt@think-slick.de",
     "url": "https://think-slick.de"
   },
-  "homepage": "https://git.slickservice.eu/Idea2Self/agent-skills",
-  "repository": {
-    "type": "git",
-    "url": "https://git.slickservice.eu/Idea2Self/agent-skills.git"
-  },
-  "license": "MIT",
   "plugins": [
     {
       "name": "klarheit-mit-idea2self",
@@ -24,6 +19,7 @@
         "url": "https://think-slick.de"
       },
       "homepage": "https://git.slickservice.eu/Idea2Self/agent-skills",
+      "repository": "https://git.slickservice.eu/Idea2Self/agent-skills.git",
       "license": "MIT",
       "keywords": [
         "idea2self",