feat: serve docs flat at /<repo>/ with no redirects

- collect.py copies each repo's built site contents directly to a
  top-level <repo>/ dir (was libs|apis|wiki/<repo>/site nesting)
- nginx uses `index index.html lib/index.html api/index.html` so
  /dagpipe/ -> lib/index.html, /auth-server/ -> api/index.html are
  served internally with no redirects
- _index regenerates links against the flat layout
  (/dagpipe/lib/, /auth-server/api/, /mongo-ops/, /blog/...)
- config.yml static entries point at vendored blog/ + media-manager/
- Dockerfile copies per-repo dirs flat into the nginx html root
- removed stale libs/, apis/, wiki/, tutorials/ category trees

dagpipe/mcp/nav.json

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