Revert "Delete vendor/ and the route proxy's: the build module fetches the modules, the root image builds with -mod=mod (issue 1305, C6)"

This reverts commit 9c4bf1f08b.

go.mod

@@ -31,6 +31,8 @@ require (
 
 // The node-engine's own validator (mesh-host/validate, novox/hq to-be 45 D1): one validator, the host's.
 // The host's module path names no forge a build can fetch from, so the module is read from the one
-// that holds it, at the host's commit — fetched by the build module over SSH like every module (novox/hq ADR 0503 §4,
-// issue 1305): no vendor/ directory holds a copy. A pin moved changes this line and go.sum, and nothing else.
+// that holds it, at the host's commit — **once, by whoever moves the pin, into vendor/**, which is
+// committed. Every build (the build agent's `go build`, the Dockerfile) compiles from vendor/ and
+// fetches nothing; go refuses to build when vendor/ and this file disagree, so a pin moved without
+// `go mod vendor` fails loudly, at once, everywhere.
 replace github.com/novox/mesh-host => git.novox.be/novox/mesh-host v0.0.0-20261018171808-9d9e3a46c4f5