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/TenantRequests.cs

@@ -0,0 +1,71 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace FlatRender.IdentitySvc.Models.Requests;
+
+public record CreateTenantRequest(
+    [Required] string Slug,
+    [Required] string Name,
+    string? Kind,
+    string? ContactName,
+    [Required, EmailAddress] string ContactEmail,
+    string? ContactPhone
+);
+
+public record UpdateTenantRequest(
+    string? Name,
+    string? ContactName,
+    string? ContactEmail,
+    string? ContactPhone,
+    string? BillingEmail,
+    string[]? AllowedOrigins
+);
+
+public record TenantBrandingRequest(
+    string? DisplayName,
+    string? LogoUrl,
+    string? LogoDarkUrl,
+    string? FaviconUrl,
+    string? OgImageUrl,
+    string? PrimaryColor,
+    string? SecondaryColor,
+    string? AccentColor,
+    string? BackgroundColor,
+    string? FontFamily,
+    string? EmailFromName,
+    string? EmailFromAddress,
+    string? EmailReplyTo,
+    string? EmailFooterHtml,
+    string? SupportUrl,
+    string? TermsUrl,
+    string? PrivacyUrl,
+    bool? EmbedEnabled,
+    string[]? EmbedAllowedHosts,
+    string? WatermarkText,
+    string? WatermarkImageUrl,
+    bool? WatermarkEnabled
+);
+
+public record StartDomainVerificationRequest([Required] string Domain, string Method = "DNS_TXT");
+
+public record CreateApiKeyRequest(
+    [Required] string Name,
+    string Environment = "Live",
+    [Required] string[] Scopes = default!,
+    string[]? AllowedIps = null,
+    int RateLimitRpm = 60,
+    DateTime? ExpiresAt = null
+);
+
+public record RevokeApiKeyRequest(string? Reason);
+
+public record ValidateApiKeyRequest(
+    [Required] string KeyPrefix,
+    [Required] string KeyHash,
+    string? IpAddress
+);
+
+public record CreateWebhookRequest(
+    [Required] string Name,
+    [Required] string Url,
+    [Required] string[] Events
+);