🏗️ reshape repo into reliquary marketplace

The single ai-skills plugin becomes plugins/g4b_ai/ inside a
reliquary-named Claude marketplace. Root README/CLAUDE.md now
describe the marketplace; the plugin's own docs move alongside it.
This makes room for additional themed plugins and non-Claude
formats in parallel.

.claude-plugin/marketplace.json

@@ -1,14 +1,14 @@
 {
-  "name": "ai-skills",
+  "name": "reliquary",
   "owner": {
     "name": "Gabor Körber",
     "email": "gab@g4b.org"
   },
   "plugins": [
     {
-      "name": "ai-skills",
-      "source": "./",
-      "description": "Personal Claude Code skills: workpad, research-tree, implementation-orchestration, markdown-embedded-svg"
+      "name": "g4b_ai",
+      "source": "./plugins/g4b_ai",
+      "description": "Gabor's personal Claude Code skills: workpad, research-tree, implementation-orchestration, markdown-embedded-svg"
     }
   ]
 }

.claude-plugin/plugin.json

@@ -1,9 +0,0 @@
-{
-  "name": "ai-skills",
-  "version": "0.1.0",
-  "description": "Gabor's personal Claude Code skills (workpad, research-tree, implementation-orchestration, markdown-embedded-svg)",
-  "author": {
-    "name": "Gabor Körber",
-    "email": "gab@g4b.org"
-  }
-}