feat: allow pass hostname in docker env

[tomerqodo]

Benchmark PR from qodo-benchmark#419

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Note

Adds optional hostname override for SMTP HELO/EHLO and propagates it through configuration and runtime.

• New SMTP_LOCAL_HOSTNAME in MailConfig and documented in api/.env.example, integration test .env.example, and docker/.env.example
• docker-compose.yaml passes SMTP_LOCAL_HOSTNAME to the API service
• SMTPClient.send now sets local_hostname when creating smtplib.SMTP/SMTP_SSL and uses it for EHLO in STARTTLS flow
• Unit/integration tests updated to expect local_hostname parameter (ANY) in SMTP constructors

^{Written by Cursor Bugbot for commit 3e5625b. Configure here.}