Restore forgot-password email delivery in Docker deployments

[Atlas-SZ]

Fixes #235

Summary

• inject .env mail/reset settings into the Docker backend service with env_file
• fix async email background-job execution when Starlette runs the task in a threadpool without a running event loop
• add a regression test covering the no-running-loop path

Root Cause

There were two separate issues affecting forgot-password in Docker deployments:

1. docker-compose.yml did not inject the SMTP and reset-password related values from .env into the backend container, so the backend could start without the expected
   mail configuration.
2. The forgot-password email job was dispatched through a sync background-task bridge that called asyncio.create_task() from a Starlette threadpool worker, which raised
   RuntimeError: no running event loop and prevented the mail from being sent even though the API returned a success response.

Changes

• added env_file: ./.env to the Docker backend service
• updated run_background_email_job() to:
  • use asyncio.run() when no running event loop exists
  • keep the existing fire-and-forget path when a loop is available
• added a regression test to ensure awaitable email jobs execute correctly from a sync context without an active event loop

Test Plan

• cd backend && .venv/bin/python -m pytest tests/test_password_reset_and_notifications.py -k 'run_background_email_job_executes_awaitable_without_running_loop or hides_email_delivery_failures or send_system_email_uses_configured_timeout' -q
• docker compose config | rg 'SYSTEM_EMAIL_FROM_ADDRESS|PUBLIC_BASE_URL|PASSWORD_RESET_TOKEN_EXPIRE_MINUTES'
• Verify forgot-password end-to-end on the deployed Docker environment

Notes

• This PR does not change the forgot-password response semantics.
• This PR is scoped only to the Docker env injection issue and the background email task execution bug.

[Atlas-SZ]

已实测，合并前辛苦再测一下。

[wisdomqin]

Thanks for the thorough analysis and the well-structured PR — the root cause diagnosis is accurate for the architecture you were working against.

After reviewing our current codebase, both issues have already been addressed through a different architectural approach:

Bug 1 (SMTP env vars not injected into Docker):
Our SMTP configuration has been fully migrated to the UI/database layer. resolve_email_config_async() reads exclusively from the system_email_platform key in the system_settings table, with no environment variable fallback. There are no SMTP-related fields in config.py, so docker-compose.yml not injecting them is intentional — there is nothing to inject.

Bug 2 (async email job / no running event loop):
The forgot-password endpoint uses Starlette's BackgroundTasks.add_task() with the async def send_password_reset_email coroutine directly. Starlette detects coroutine functions and awaits them within the ASGI event loop, so the RuntimeError: no running event loop path is not reachable in our setup.

Because both fixes are already covered by the current implementation, we will close this PR. We appreciate the effort and the regression test — the test structure is clean and the PR description is a good reference.