Initial VTuber Awards implementation

Backend/README.md

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+# Backend
+
+## PostgreSQL
+
+The API targets PostgreSQL through EF Core 8 and `Npgsql.EntityFrameworkCore.PostgreSQL`.
+
+Default local development connection string:
+
+```text
+Host=localhost;Port=5433;Database=vtuber_star_awards_dev;Username=postgres;Password=postgres
+```
+
+You can override it with:
+
+- `Backend/appsettings.Development.json`
+- environment variable `VTSA_POSTGRES`
+
+If Docker is available locally, start a dev database from the repository root with:
+
+```bash
+docker compose -f docker-compose.dev.yml up -d
+```
+
+## Commands
+
+Restore and build:
+
+```bash
+dotnet restore
+dotnet build
+```
+
+Create a migration:
+
+```bash
+dotnet ef migrations add InitialCreate
+```
+
+Generate a SQL migration script:
+
+```bash
+dotnet ef migrations script 0 20260617060000_InitialCreate --output Migrations/InitialCreate.sql
+```
+
+Apply migrations once PostgreSQL is running:
+
+```bash
+dotnet ef database update
+```
+
+Fallback bootstrap if `dotnet ef` is not usable in the current environment:
+
+```bash
+psql "Host=localhost Port=5433 Database=vtuber_star_awards_dev Username=postgres Password=postgres" -f Migrations/InitialCreate.manual.sql
+```
+
+Run the API:
+
+```bash
+ASPNETCORE_ENVIRONMENT=Development dotnet run
+```
+
+Check the API and database wiring:
+
+```bash
+curl http://localhost:5084/api/health
+curl http://localhost:5084/api/health/database
+```
+
+Development auth/session:
+
+```bash
+curl -X POST http://localhost:5084/api/auth/dev-login \
+  -H "Content-Type: application/json" \
+  -d '{"twitchUserId":"admin_demo","displayName":"Admin Demo","role":"admin"}'
+```