Move scripts to docgen/, remove possess_flow.png

- docgen/: generate.py, ue_parser.py, ue_markdown.py, ue_mcp_server.py
- .mcp.json: update server path to docgen/ue_mcp_server.py
- Update CLAUDE.md and README paths accordingly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.mcp.json

@@ -2,7 +2,7 @@
   "mcpServers": {
     "ue-docs": {
       "command": "python",
-      "args": ["ue_mcp_server.py"]
+      "args": ["docgen/ue_mcp_server.py"]
     }
   }
 }