server.json: registry caps description at 100 chars

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: conorbronsdon

server.json

@@ -2,7 +2,7 @@
   "$schema": "https://static.modelcontextprotocol.io/schemas/2025-12-11/server.schema.json",
   "name": "io.github.conorbronsdon/substack-mcp",
   "title": "Substack MCP Server",
-  "description": "MCP server for Substack — read posts, manage drafts, upload images, publish Notes. Long-form posts are draft-only (no publish or delete); Notes publish immediately. Uses unofficial Substack API.",
+  "description": "Substack MCP server: posts are draft-only by design; short-form Notes publish immediately.",
   "repository": {
     "url": "https://github.com/conorbronsdon/substack-mcp",
     "source": "github"