fix(worker): Prevent stale DB connection in apply_async routing

[sentry]

This PR addresses an OperationalError: server closed the connection unexpectedly occurring in the app.tasks.upload.Upload Celery task, specifically during the apply_async method's task routing logic.

Root Cause:
The apply_async override in apps/worker/tasks/base.py queries the PostgreSQL read replica via _get_user_plan_from_task to determine task routing. The database connection used for this query was opened at the start of the long-running Upload task and was held open without activity. By the time apply_async was invoked to dispatch follow-up tasks, the read replica had terminated the idle connection server-side, leading to the OperationalError when the query was attempted.

Solution:
To resolve this, the apply_async method in apps/worker/tasks/base.py has been modified to:

1. Explicitly call get_db_session.remove() at the beginning of the method. This discards any potentially stale SQLAlchemy scoped session (and its underlying connection) that might have been held open during the task's execution.
2. Re-acquire a fresh database session for the subsequent routing queries (_get_user_plan_from_task and _get_ownerid_from_task).
3. Implement a retry mechanism: if an OperationalError still occurs during the initial attempt to query the database for routing, the session is removed again, and the query is retried once. This provides additional robustness against transient connection issues.

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Fixes WORKER-YYY

[codecov]

Codecov Report

❌ Patch coverage is 45.45455% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.88%. Comparing base (701e991) to head (fdaac27).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/worker/tasks/base.py	45.45%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1427      +/-   ##
==========================================
- Coverage   91.89%   91.88%   -0.02%     
==========================================
  Files        1325     1325              
  Lines       50868    50876       +8     
  Branches     1626     1626              
==========================================
+ Hits        46744    46746       +2     
- Misses       3818     3824       +6     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.54% <45.45%> (-0.02%)	⬇️
workerunit	90.34% <45.45%> (-0.04%)	⬇️

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[codecov-notifications]

Codecov Report

❌ Patch coverage is 45.45455% with 6 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/worker/tasks/base.py	45.45%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (45.45%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

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