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>

backend/contracts/events/file.yaml

@@ -0,0 +1,114 @@
+# =====================================================================
+# File Events — published by File Service
+# =====================================================================
+events:
+
+  file.uploaded.v1:
+    routing_key: file.uploaded.v1
+    description: A file upload has completed and is ready to use.
+    payload:
+      type: object
+      required: [file_id, user_id, file_type, size_bytes, url]
+      properties:
+        file_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid }
+        user_id: { type: string, format: uuid }
+        folder_id: { type: string, format: uuid, nullable: true }
+        name: { type: string }
+        file_type: { type: string, enum: [Video, Image, Audio, Voiceover, Document, Other] }
+        mime_type: { type: string }
+        size_bytes: { type: integer, format: int64 }
+        url: { type: string }
+        thumbnail_url: { type: string, nullable: true }
+        duration_sec: { type: number, nullable: true }
+        width: { type: integer, nullable: true }
+        height: { type: integer, nullable: true }
+        source:
+          type: string
+          enum: [upload, export, snapshot, voiceover_record, stock]
+
+  file.processed.v1:
+    routing_key: file.processed.v1
+    description: Post-upload processing (thumbnail, waveform, transcode) finished.
+    payload:
+      type: object
+      required: [file_id, status]
+      properties:
+        file_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid }
+        user_id: { type: string, format: uuid }
+        status: { type: string, enum: [Ready, Failed, Quarantined] }
+        thumbnail_url: { type: string, nullable: true }
+        waveform_generated: { type: boolean }
+        duration_sec: { type: number, nullable: true }
+        error_message: { type: string, nullable: true }
+
+  file.deleted.v1:
+    routing_key: file.deleted.v1
+    payload:
+      type: object
+      required: [file_id, user_id, size_bytes_freed]
+      properties:
+        file_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid }
+        user_id: { type: string, format: uuid }
+        size_bytes_freed: { type: integer, format: int64 }
+        deleted_by:
+          type: string
+          enum: [user, auto_cleanup, admin, quota_exceeded]
+
+  file.quota_warning.v1:
+    routing_key: file.quota_warning.v1
+    description: User passed 90% of storage quota.
+    payload:
+      type: object
+      required: [user_id, used_bytes, quota_bytes, percent_used]
+      properties:
+        user_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid }
+        used_bytes: { type: integer, format: int64 }
+        quota_bytes: { type: integer, format: int64 }
+        percent_used: { type: number }
+
+  file.quota_exceeded.v1:
+    routing_key: file.quota_exceeded.v1
+    description: User hit 100% storage quota — uploads blocked.
+    payload:
+      type: object
+      required: [user_id, used_bytes, quota_bytes]
+      properties:
+        user_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid }
+        used_bytes: { type: integer, format: int64 }
+        quota_bytes: { type: integer, format: int64 }
+        attempted_upload_size_bytes: { type: integer, format: int64, nullable: true }
+
+  file.cleanup.scheduled.v1:
+    routing_key: file.cleanup.scheduled.v1
+    description: An entity has been queued for automatic deletion.
+    payload:
+      type: object
+      required: [cleanup_id, entity_type, entity_id, scheduled_delete_at]
+      properties:
+        cleanup_id: { type: string, format: uuid }
+        tenant_id: { type: string, format: uuid, nullable: true }
+        user_id: { type: string, format: uuid, nullable: true }
+        entity_type:
+          type: string
+          enum: [Export, TempRenderFolder, OrphanedFile, UnusedUpload, SnapshotExpired]
+        entity_id: { type: string, format: uuid }
+        scheduled_delete_at: { type: string, format: date-time }
+        notify_user_at: { type: string, format: date-time, nullable: true }
+
+  file.cleanup.executed.v1:
+    routing_key: file.cleanup.executed.v1
+    payload:
+      type: object
+      required: [cleanup_id, status, bytes_freed]
+      properties:
+        cleanup_id: { type: string, format: uuid }
+        entity_type: { type: string }
+        entity_id: { type: string, format: uuid }
+        status: { type: string, enum: [Done, Skipped, Failed] }
+        bytes_freed: { type: integer, format: int64 }
+        error_message: { type: string, nullable: true }