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

prisma.config.ts

@@ -0,0 +1,11 @@
+import { defineConfig } from "prisma/config";
+
+export default defineConfig({
+  schema: "prisma/schema.prisma",
+  migrations: {
+    path: "prisma/migrations",
+  },
+  datasource: {
+    url: process.env["DATABASE_URL"] || "postgresql://vixtix:vixtix_secret@localhost:5433/vixtix",
+  },
+});