refactor: serve MCP bundles under <name>/mcp with nginx guard; rename core->mcp_server

- collect.py: copy repo MCP bundles to ROOT/<name>/mcp (instead of ROOT/mcp/<name>); add nginx location guard to deny /<name>/mcp/
- config.py: bundle roots now point to <repo>/mcp and standards/mcp for static bundles
- Rename core.py -> mcp_server.py and update imports in main.py and registry.py
- Dockerfile: per-repo MCP COPYs under /app/<name>/mcp, drop blog copy; add ports 8008/8009 in .drone.yml
- Restore standards/mcp/libraries.json from git for registry server

dagpipe/mcp/nav.json

@@ -0,0 +1,26 @@
+[
+  {
+    "module": "dagpipe",
+    "resource": "docs://modules/dagpipe"
+  },
+  {
+    "module": "dagpipe.engine",
+    "resource": "docs://modules/dagpipe.engine"
+  },
+  {
+    "module": "dagpipe.graph",
+    "resource": "docs://modules/dagpipe.graph"
+  },
+  {
+    "module": "dagpipe.node",
+    "resource": "docs://modules/dagpipe.node"
+  },
+  {
+    "module": "dagpipe.state",
+    "resource": "docs://modules/dagpipe.state"
+  },
+  {
+    "module": "dagpipe.yaml_loader",
+    "resource": "docs://modules/dagpipe.yaml_loader"
+  }
+]