feat: Setup database modules and migrations

[ayo-ola0710]

What was done

Optimized tool selectionI added a PostgreSQL + TypeORM foundation: installed typeorm, pg, @nestjs/typeorm, class-validator, and class-transformer; created TypeORM config and DataSource in src/database/database.config.ts and src/database/data.source.ts; added a DatabaseModule (src/database/database.module.ts) and wired it into src/app.module.ts; implemented seven entities (User, NGO, Donation, Volunteer, Task, TaskSubmission, Reward) under src/entities/ with relations and timestamps; created an initial migration migrations/1720569600000-CreateInitialSchema.ts; added a .env.example and a DATABASE_SETUP.md with setup/migration instructions; and updated package.json with migration scripts so you can run npm run migration:run to apply the schema.