export-github: exclude mcp/ from public publication

The MCP server README names Claude Desktop / Claude Code (it is an MCP
server for those clients), which trips the scrub gate. It is a standalone
local tool distributed via pxe-images/mcp/ + setup-mcp.cmd, not part of the
shipped product, so exclude it from the public repo like docs/ and tools/.

tools/export-github.sh

@@ -35,6 +35,7 @@ rsync -a --delete \
   --exclude '.gitea' \
   --exclude 'docs' \
   --exclude 'tools' \
+  --exclude 'mcp' \
   --exclude 'start-api.sh' \
   --exclude 'start-ui.sh' \
   --exclude 'CLAUDE.md' \