feat(nostr): nostr-based account registration and verification

Rebuilt the nostr registration feature cleanly on top of current ergo
mainline (origin/master), dropping the stale ergo reversions that were
entangled in the original squashed branch.

- New irc/nostr package: NIP-04/NIP-17 DMs, NIP-05 resolution, relay
  connect/auth, and identifier helpers.
- Registration/verification via nostr: parseCallback auto-detects nostr
  identifiers (NIP-05, npub, hex pubkey) and dispatches a verification DM.
- Nostr-based cloaked hostnames for accounts (opt-in via
  ip-cloaking.nostr-hostnames), applied at the account-cloak sites.
- Config: accounts.registration.nostr-verification and the
  nostr-hostnames cloak option, with matching default.yaml and help text.
- Adds github.com/nbd-wtf/go-nostr and vendored dependencies.

vendor/github.com/coder/websocket/internal/errd/wrap.go

@@ -0,0 +1,14 @@
+package errd
+
+import (
+	"fmt"
+)
+
+// Wrap wraps err with fmt.Errorf if err is non nil.
+// Intended for use with defer and a named error return.
+// Inspired by https://github.com/golang/go/issues/32676.
+func Wrap(err *error, f string, v ...interface{}) {
+	if *err != nil {
+		*err = fmt.Errorf(f+": %w", append(v, *err)...)
+	}
+}