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/file/vendor/github.com/cloudwego/base64x/Makefile

@@ -0,0 +1,29 @@
+.PHONY: all clean
+
+CFLAGS := -mavx
+CFLAGS += -mavx2
+CFLAGS += -mno-bmi
+CFLAGS += -mno-red-zone
+CFLAGS += -fno-asynchronous-unwind-tables
+CFLAGS += -fno-stack-protector
+CFLAGS += -fno-exceptions
+CFLAGS += -fno-builtin
+CFLAGS += -fno-rtti
+CFLAGS += -nostdlib
+CFLAGS += -O3
+
+NATIVE_ASM := $(wildcard native/*.S)
+NATIVE_SRC := $(wildcard native/*.h)
+NATIVE_SRC += $(wildcard native/*.c)
+
+all: native_amd64.s
+
+clean:
+	rm -vf native_text_amd64.go native_subr_amd64.go output/*.s
+
+native_amd64.s: ${NATIVE_SRC} ${NATIVE_ASM} native_amd64.go
+	mkdir -p output
+	clang ${CFLAGS} -S -o output/native.s native/native.c
+	python3 tools/asm2asm/asm2asm.py -r native_amd64.go output/native.s ${NATIVE_ASM}
+	awk '{gsub(/Text__native_entry__/, "text__native_entry__")}1' native_text_amd64.go > native_text_amd64.go.tmp && mv native_text_amd64.go.tmp native_text_amd64.go
+	awk '{gsub(/Funcs/, "funcs")}1' native_subr_amd64.go > native_subr_amd64.go.tmp && mv native_subr_amd64.go.tmp native_subr_amd64.go