Initial lookbook implementation

Pinterest-style visual bookmarking app with:
- URL metadata extraction (OG/Twitter meta, oEmbed fallback)
- Image caching in Postgres with 480px thumbnails
- Multi-tag filtering with Ctrl/Cmd for OR mode
- Fuzzy tag suggestions and inline tag editing
- Browser console auth() with first-use password setup
- Brutalist UI with Commit Mono font and Pico CSS
- Light/dark mode via browser preference

vendor/github.com/jackc/pgx/v5/pgproto3/authentication_gss.go

@@ -0,0 +1,58 @@
+package pgproto3
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+
+	"github.com/jackc/pgx/v5/internal/pgio"
+)
+
+type AuthenticationGSS struct{}
+
+func (a *AuthenticationGSS) Backend() {}
+
+func (a *AuthenticationGSS) AuthenticationResponse() {}
+
+func (a *AuthenticationGSS) Decode(src []byte) error {
+	if len(src) < 4 {
+		return errors.New("authentication message too short")
+	}
+
+	authType := binary.BigEndian.Uint32(src)
+
+	if authType != AuthTypeGSS {
+		return errors.New("bad auth type")
+	}
+	return nil
+}
+
+func (a *AuthenticationGSS) Encode(dst []byte) ([]byte, error) {
+	dst, sp := beginMessage(dst, 'R')
+	dst = pgio.AppendUint32(dst, AuthTypeGSS)
+	return finishMessage(dst, sp)
+}
+
+func (a *AuthenticationGSS) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Data []byte
+	}{
+		Type: "AuthenticationGSS",
+	})
+}
+
+func (a *AuthenticationGSS) UnmarshalJSON(data []byte) error {
+	// Ignore null, like in the main JSON package.
+	if string(data) == "null" {
+		return nil
+	}
+
+	var msg struct {
+		Type string
+	}
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return err
+	}
+	return nil
+}