Implement .env parsing for network configuration

[Code-Paragon]

Problem

The frontend currently lacks a standardized way to manage different deployment environments, meaning RPC URLs and Contract IDs will have to be hardcoded when integrating the SDK.

Expected behavior

A src/config.ts file is created to parse and validate environment variables (e.g., NEXT_PUBLIC_RPC_URL, NEXT_PUBLIC_CONTRACT_ID) with strict fallbacks.

Files to update

• src/config.ts (create)
• .env.example (create)

Project relevance

Ensures secure, dynamic deployments across local, testnet, and mainnet environments without committing sensitive configuration strings to the repository.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• .env.example is documented with required configuration keys
• No TypeScript, lint, test, or build errors