migrate: replace pg with Prisma ORM

- Add prisma/schema.prisma with Project/Task models, enums, and relations
- Create src/lib/db.ts singleton Prisma client
- Refactor all 5 API routes to use Prisma queries
- Replace migrate.ts with seed.ts for initial data
- Update Dockerfile for Prisma lifecycle (copy generated client)
- Update tsconfig.json with @/generated/* path alias
- Remove pg and @types/pg dependencies
- Add prisma.config.ts for Prisma 6 config
- Update .gitignore for generated Prisma client

tsconfig.json

@@ -19,7 +19,8 @@
       }
     ],
     "paths": {
-      "@/*": ["./src/*"]
+      "@/*": ["./src/*"],
+      "@/generated/*": ["./src/generated/*"]
     }
   },
   "include": [
@@ -30,5 +31,5 @@
     ".next/dev/types/**/*.ts",
     "**/*.mts"
   ],
-  "exclude": ["node_modules"]
+  "exclude": ["node_modules", "vitest.config.ts"]
 }