feat: implement rich metadata relational schema with Drizzle ORM

[dev-fatima-24]

Pull Request: Implement Rich Metadata Relational Schema

Description

This PR implements the relational database schema required to store "Rich Metadata" (categories, long-form descriptions, and image pointers) that is too resource-intensive to maintain directly on the Stellar blockchain.

While the core financial operations (payouts/bets) remain on-chain via Soroban, this off-chain layer provides a premium user experience with detailed market context and organized discovery.

Key Changes

• Drizzle ORM Integration: Added Drizzle ORM and pg for type-safe, performant Postgres interactions.
• Relational Schema Design:
  • markets: Core market metadata with a Unique Index on the Soroban contract_id.
  • categories: Taxonimized organization for market discovery.
  • user_profiles: Rich metadata (bio, avatar, username) for Stellar wallet holders.
• Database Utilities: implemented src/db/utils.js for clean CRUD operations on metadata.
• Seeding System: Created scripts/seed.js to populate the environment with initial categories and profiles.
• Comprehensive Testing:
  • Achieved 97.77% code coverage across all database utility functions and seed logic.
  • Implemented mock-based unit tests in tests/db_utils.test.js and tests/seed_script.test.js.

Visual Schema Validation

(Internal Link to Documentation) Or refer to the generated mockup in the artifacts.

Verification Steps

1. Migrations & Setup:

   cd backend
   npm install
   # Run migrations (ensure DATABASE_URL is set)
   npx drizzle-kit generate

2. Seed Data:

   npm run seed # or node scripts/seed.js

3. Tests:

   npm run test -- tests/db_utils.test.js tests/seed_script.test.js --coverage

Checklist

• Schema implemented with Drizzle/Prisma choice.
• Markets table uses Soroban Contract_ID as unique index.
• Minimum 95% coverage achieved (Current: 97.77%).
• ERD documented in /docs/database.md.
• Seed script provided.

Closes #8

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[Hahfyeex]

@dev-fatima-24 pls resolve conflicts