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/render/vendor/github.com/dustin/go-humanize/commaf.go

@@ -0,0 +1,41 @@
+//go:build go1.6
+// +build go1.6
+
+package humanize
+
+import (
+	"bytes"
+	"math/big"
+	"strings"
+)
+
+// BigCommaf produces a string form of the given big.Float in base 10
+// with commas after every three orders of magnitude.
+func BigCommaf(v *big.Float) string {
+	buf := &bytes.Buffer{}
+	if v.Sign() < 0 {
+		buf.Write([]byte{'-'})
+		v.Abs(v)
+	}
+
+	comma := []byte{','}
+
+	parts := strings.Split(v.Text('f', -1), ".")
+	pos := 0
+	if len(parts[0])%3 != 0 {
+		pos += len(parts[0]) % 3
+		buf.WriteString(parts[0][:pos])
+		buf.Write(comma)
+	}
+	for ; pos < len(parts[0]); pos += 3 {
+		buf.WriteString(parts[0][pos : pos+3])
+		buf.Write(comma)
+	}
+	buf.Truncate(buf.Len() - 1)
+
+	if len(parts) > 1 {
+		buf.Write([]byte{'.'})
+		buf.WriteString(parts[1])
+	}
+	return buf.String()
+}