Vendor every dependency, so no build fetches the host's validator (hq to-be 45 D1)

The controller imports mesh-host/validate through a replace onto the forge
that holds it, and every build — the build agent's go build in a fresh
toolchain container, the Dockerfile's go mod download — would have fetched
it through the public proxy and checksum database at build time: a merge
breaking main on the network, the class Phase 1 removes. vendor/ is
committed; go builds from it with nothing fetched, and refuses to build
when it and go.mod disagree, so a pin moved without go mod vendor fails at
once. The Dockerfile copies vendor/ and builds with GOPROXY=off.

vendor/github.com/jackc/puddle/v2/doc.go

@@ -0,0 +1,11 @@
+// Package puddle is a generic resource pool with type-parametrized api.
+/*
+
+Puddle is a tiny generic resource pool library for Go that uses the standard
+context library to signal cancellation of acquires. It is designed to contain
+the minimum functionality a resource pool needs that cannot be implemented
+without concurrency concerns. For example, a database connection pool may use
+puddle internally and implement health checks and keep-alive behavior without
+needing to implement any concurrent code of its own.
+*/
+package puddle