fix: remove quote characters from empty dotenv values in .env.example

[coderabbitai]

Summary

All empty-string dotenv values in .env.example currently use quoted assignment (e.g., KEY=''), which triggers a QuoteCharacter warning from dotenv-linter. They should be changed to unquoted empty assignments (e.g., KEY=) to satisfy the linter.

Affected variables

All variables with ='' in .env.example, including (but not limited to):

• DATA_CONTRACT_ID
• RECIPIENT_ID
• RECIPIENT_PLATFORM_ADDRESS
• WITHDRAWAL_ADDRESS
• DOCUMENT_ID
• DISABLE_KEY_ID
• NAME_LABEL
• NFT_CONTRACT_ID
• NFT_DOCUMENT_ID

References

• Raised during review of PR feat: migrate send-funds tutorial to new evo-sdk #65: feat: migrate send-funds tutorial to new evo-sdk #65
• Comment: feat: migrate send-funds tutorial to new evo-sdk #65 (comment)
• Requested by: @thephez