chore(plugin): commit baseline plugin state pre-refactor

Baseline commit before splitting klarheit-mit-idea2self into router +
7 atomic workflow-skills. Captures the monolithic skill (1.671 LOC,
8 workflows, 5 references, 2 templates) as the starting point so
subsequent steps can use git mv with rename detection.

Files added:
- .claude-plugin/plugin.json + marketplace.json
- README.md (plugin overview, ex-skills/README.md)
- skills/klarheit-mit-idea2self/ (full monolith)

Refactor tracked in parent repo: DEC-0010,
agentbrain/memory/plans/engineering/2026-05-19-i2s-skill-split.md.

.claude-plugin/marketplace.json

@@ -0,0 +1,20 @@
+{
+  "name": "idea2self-ecosystem",
+  "description": "Idea2Self – Von vager Idee zu messbarem nächsten Schritt.",
+  "owner": {
+    "name": "Philipp Sieder",
+    "email": "kontakt@think-slick.de"
+  },
+  "plugins": [
+    {
+      "name": "klarheit-mit-idea2self",
+      "description": "KI-gestützter Facilitator für Ideenentwicklung, Validierung und Umsetzungsplanung mit Design Thinking, Lean Startup und WOOP.",
+      "version": "1.0.0",
+      "source": "./",
+      "author": {
+        "name": "Philipp Sieder",
+        "email": "kontakt@think-slick.de"
+      }
+    }
+  ]
+}