feat: V2 microservices stack — backend services, gateway, JWT auth

Add full V2 architecture: identity, content, studio (.NET 10) and file,
render, notification, gateway (Go) services with vendored deps, plus DB
migrations, event/API contracts, and an init-db script.

Wire the Next.js frontend to the gateway: server-side JWT auth routes
(login/register/refresh/logout/me), gateway fetch helper, and session/
cookie/jwt helpers under src/lib.

Containerize the stack via docker-compose.v2.yml and per-service
Dockerfiles. Base images resolve through a Nexus mirror (Docker Hub) and
MCR directly; npm/NuGet pull from Nexus groups. Self-host fonts via
next/font/local to avoid Google Fonts (geo-blocked).

Add CI workflow and ignore .env.v2, *.stackdump, and .NET bin/obj.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

services/notification/vendor/github.com/google/uuid/sql.go

@@ -0,0 +1,59 @@
+// Copyright 2016 Google Inc.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package uuid
+
+import (
+	"database/sql/driver"
+	"fmt"
+)
+
+// Scan implements sql.Scanner so UUIDs can be read from databases transparently.
+// Currently, database types that map to string and []byte are supported. Please
+// consult database-specific driver documentation for matching types.
+func (uuid *UUID) Scan(src interface{}) error {
+	switch src := src.(type) {
+	case nil:
+		return nil
+
+	case string:
+		// if an empty UUID comes from a table, we return a null UUID
+		if src == "" {
+			return nil
+		}
+
+		// see Parse for required string format
+		u, err := Parse(src)
+		if err != nil {
+			return fmt.Errorf("Scan: %v", err)
+		}
+
+		*uuid = u
+
+	case []byte:
+		// if an empty UUID comes from a table, we return a null UUID
+		if len(src) == 0 {
+			return nil
+		}
+
+		// assumes a simple slice of bytes if 16 bytes
+		// otherwise attempts to parse
+		if len(src) != 16 {
+			return uuid.Scan(string(src))
+		}
+		copy((*uuid)[:], src)
+
+	default:
+		return fmt.Errorf("Scan: unable to scan type %T into UUID", src)
+	}
+
+	return nil
+}
+
+// Value implements sql.Valuer so that UUIDs can be written to databases
+// transparently. Currently, UUIDs map to strings. Please consult
+// database-specific driver documentation for matching types.
+func (uuid UUID) Value() (driver.Value, error) {
+	return uuid.String(), nil
+}