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/content/FlatRender.ContentSvc/Domain/Enums/Enums.cs

@@ -0,0 +1,18 @@
+namespace FlatRender.ContentSvc.Domain.Enums;
+
+public enum ChooseMode { FIX, FLEXIBLE, MockUp, MusicVisualizer, VoiceOver }
+public enum ResolutionKind { HD, FullHD, TwoK, FourK }
+public enum SceneKind { Normal, Config, DesignStart, DesignEnd }
+public enum ContentElementType
+{
+    Text, TextArea, Media, Audio, Voiceover,
+    CheckBox, DropDown, Fill, Color, Number,
+    Date, Toggle, Slider, Counter, Hidden
+}
+public enum JustifyKind { LEFT_JUSTIFY, CENTER_JUSTIFY, RIGHT_JUSTIFY, FULL_JUSTIFY }
+public enum AiInputType { None, TitleSuggest, BodySuggest, TranslateRtl, TranslateLtr, RemoveBG, UpscaleImage, TTS }
+public enum RepeatSortStrategy { Manual, Alphabetical, Numerical, InsertOrder }
+public enum AttrValueKind { fill, stroke, tracking, dropshadow }
+public enum BlogKind { Blog, Landing }
+public enum SlideType { Hero, Promo, Tutorial, Category, Custom }
+public enum ContainerFavoriteKind { Container }