setting TANGLED_DEV=true now lets you work on tangled without creating
ngrok/localtunnel tunnels.

NixOS 24.11 doesn't provide go-1.24 which is now required for this
project.

Additionally fix the `CGO_ENABLED` warnings that comes with the newer
nixpkgs version.

Lets us use it without an import cycle.

This serves the go-import meta tag if the user-agent is
Go-http-client/1.1 and there's a ?go-get=1 query parameter present. This
should run before the router 404's a path that technically doesn't exist
like tangled.sh/foo.com/some-go/v5.

the current transaction model only rollsback on db failures. this
changeset makes the transaction encapsulate the entire NewPull flow. if
creating the pds record fails, the db is still rolled back.