Initial open-source release (MIT): image2api AI gateway

Full Go backend + Vue 3 frontend, OpenAI-compatible API, multi-provider
account pools, billing/admin, Docker one-command deploy with auto HTTPS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/README.md

@@ -0,0 +1,55 @@
+# Vivid AI Backend
+
+Go backend for `vivid-ai`, using:
+
+- Gin
+- GORM
+- PostgreSQL
+- Redis
+
+## Current scope
+
+This is an in-progress rewrite. The current skeleton already includes:
+
+- app bootstrap
+- PostgreSQL and Redis initialization
+- GORM auto-migrations
+- session storage in Redis
+- image access control for `/images/:user/:name`
+- public site endpoint: `/admin/api/site`
+- public showcase endpoint: `/admin/api/showcase`
+- session-based auth endpoint: `/admin/api/auth/me`
+
+## Environment
+
+Set these before running:
+
+```powershell
+$env:POSTGRES_DSN="host=127.0.0.1 user=postgres password=postgres dbname=vivid_ai port=5432 sslmode=disable TimeZone=Asia/Shanghai"
+$env:REDIS_ADDR="127.0.0.1:6379"
+$env:HTTP_ADDR=":6061"
+```
+
+Optional:
+
+```powershell
+$env:APP_ENV="development"
+$env:APP_TITLE="Vivid AI"
+$env:SESSION_COOKIE_NAME="vivid_session"
+$env:CORS_ORIGINS="http://localhost:5173,http://127.0.0.1:5173"
+```
+
+## Run
+
+```powershell
+go run ./cmd/api
+```
+
+## Notes
+
+- Generated media defaults to `../../ai-gateway/data/generated` relative to the backend working directory.
+- Private images require either:
+  - session cookie
+  - bearer session token
+  - bearer API key
+- Showcase images are public.