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/big.go

@@ -0,0 +1,31 @@
+package humanize
+
+import (
+	"math/big"
+)
+
+// order of magnitude (to a max order)
+func oomm(n, b *big.Int, maxmag int) (float64, int) {
+	mag := 0
+	m := &big.Int{}
+	for n.Cmp(b) >= 0 {
+		n.DivMod(n, b, m)
+		mag++
+		if mag == maxmag && maxmag >= 0 {
+			break
+		}
+	}
+	return float64(n.Int64()) + (float64(m.Int64()) / float64(b.Int64())), mag
+}
+
+// total order of magnitude
+// (same as above, but with no upper limit)
+func oom(n, b *big.Int) (float64, int) {
+	mag := 0
+	m := &big.Int{}
+	for n.Cmp(b) >= 0 {
+		n.DivMod(n, b, m)
+		mag++
+	}
+	return float64(n.Int64()) + (float64(m.Int64()) / float64(b.Int64())), mag
+}