docs(cursor): Add Mintlify public documentation for Cursor integration

Create searchable public documentation for Cursor users:
- cursor/index.mdx: Landing page with installation paths and quick reference
- cursor/gemini-setup.mdx: Step-by-step Gemini free tier setup guide
- cursor/openrouter-setup.mdx: OpenRouter setup with model recommendations

Add Cursor Integration navigation group to docs.json.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/public/docs.json

@@ -47,6 +47,15 @@
           "endless-mode"
         ]
       },
+      {
+        "group": "Cursor Integration",
+        "icon": "wand-magic-sparkles",
+        "pages": [
+          "cursor/index",
+          "cursor/gemini-setup",
+          "cursor/openrouter-setup"
+        ]
+      },
       {
         "group": "Best Practices",
         "icon": "lightbulb",