feat(gantry): move HTTP endpoints to Unix sockets

[Vaibhav Patel (vpatelsj)]

Summary

• move Gantry mirror, transfer, and operations HTTP servers to Unix domain sockets
• add a constrained TCP-to-UDS proxy subcommand for containerd, peer, Prometheus, and kubelet compatibility
• separate the transfer bind endpoint from its routable advertised address
• update the DaemonSet, configuration, documentation, and e2e fixture

Validation

• go test -race -count=1 ./internal/gantry/config ./internal/gantry/listener ./internal/gantry/mirror ./internal/gantry/proxy ./internal/gantry/transfer ./cmd/gantry
• scoped golangci-lint across affected Gantry packages: 0 issues
• go build ./cmd/gantry
• make gantry-manifests

Known repository issue

make gantry reaches repository-wide lint but is currently blocked by pre-existing SA5011 warnings in internal/net/routeplan/routeplan_test.go.