fix: remove onboarding-prompt claim from marketplace.json

Follow-up to the SessionStart hook removal: marketplace.json still
advertised "first-start Claude onboarding prompt" and "prompting
first-run Claude onboarding" in both the marketplace and plugin
descriptions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: raifdmueller

.claude-plugin/marketplace.json

@@ -1,15 +1,15 @@
 {
   "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
   "name": "semantic-anchors",
-  "description": "Semantic anchor skills for LLM and coding-agent onboarding, including a first-start Claude onboarding prompt",
+  "description": "Semantic anchor skills for LLM and coding-agent onboarding",
   "owner": {
     "name": "LLM Coding",
     "url": "https://github.com/LLM-Coding"
   },
   "plugins": [
     {
       "name": "semantic-anchors",
-      "description": "Semantic anchor skills for translating established methodologies, prompting first-run Claude onboarding, and installing persistent coding-agent context.",
+      "description": "Semantic anchor skills for translating established methodologies and installing persistent coding-agent context.",
       "version": "0.1.0",
       "author": {
         "name": "LLM Coding",