fix: correct Foundry env loading and Blockscout verification docs

[aproskill81]

This updates the Foundry deployment tutorial to avoid a broken deployment flow and align verification instructions with Blockscout.

Changes:

• export variables from .env before running forge script, so vm.envUint("PRIVATE_KEY") is available to Foundry
• switch verification wording from Etherscan to Blockscout
• update deploy and verify examples to use Blockscout verifier flags
• remove the unused BLOCKSCOUT_API_KEY entry from the .env example