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/identity/FlatRender.IdentitySvc/Models/Requests/AuthRequests.cs

@@ -0,0 +1,54 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace FlatRender.IdentitySvc.Models.Requests;
+
+public record RegisterRequest(
+    [Required] string TenantSlug,
+    string? Email,
+    string? PhoneNumber,
+    [Required, MinLength(8)] string Password,
+    string? FullName,
+    string? AffiliateCode,
+    bool AcceptTerms = true
+);
+
+public record LoginRequest(
+    [Required] string TenantSlug,
+    string? Email,
+    string? PhoneNumber,
+    [Required] string Password,
+    string? DeviceId,
+    string? DeviceName
+);
+
+public record OAuthLoginRequest(
+    [Required] string TenantSlug,
+    [Required] string Code,
+    string? RedirectUri
+);
+
+public record RefreshTokenRequest([Required] string RefreshToken);
+
+public record VerifyOtpRequest([Required] string Token, [Required] string Code);
+
+public record PasswordResetRequestDto([Required] string TenantSlug, string? Email, string? PhoneNumber);
+
+public record PasswordResetConfirmRequest([Required] string Token, [Required, MinLength(8)] string NewPassword);
+
+public record PasswordChangeRequest([Required] string CurrentPassword, [Required, MinLength(8)] string NewPassword);
+
+public record MfaSetupRequest([Required] string FactorType, string? Label);
+
+public record MfaVerifyRequest([Required] Guid FactorId, [Required] string Code);
+
+public record MfaChallengeRequest([Required] string MfaToken, [Required] string Code);
+
+public record PushSubscribeRequest(
+    [Required] string Endpoint,
+    [Required] PushKeys Keys,
+    string? UserAgent
+);
+
+public record PushKeys([Required] string P256dh, [Required] string Auth);
+
+public record PushUnsubscribeRequest(string? Endpoint);