Export site renders; pin the freecad-mcp MCP server

Nine 2400px views of the site model in docs/renders: an isometric, a
site plan, dimetric and trimetric, four aerial obliques from each corner,
a low approach view from the road, and two orthographic elevations.

Also hardens the freecad MCP entry added in the previous commit. It ran
"uvx freecad-mcp" unpinned, which resolves and executes whatever version
is current at every launch. Now pinned to 0.1.20 and marked optional, in
line with the ruv-swarm and flow-nexus entries alongside it.

.mcp.json

@@ -54,8 +54,11 @@
     "freecad": {
       "command": "uvx",
       "args": [
+        "--from",
+        "freecad-mcp==0.1.20",
         "freecad-mcp"
-      ]
+      ],
+      "optional": true
     }
   }
 }