fix(ci): resolve syntax and indentation errors breaking upstream main

[koushik-gupta]

What changed

This PR provides a clean, minimal fix for the remaining upstream syntax and indentation errors that were causing CI pipelines to crash on all new PRs.

Specifically, it fixes:

• Removed a rogue Git merge conflict block inside select_bandit_arm in src/model/hybrid_model.py that was causing an IndentationError.
• Fixed an IndentationError and a NameError in celery_app.py by properly unindenting the Celery configuration and referencing celery_app instead of an undefined app variable.

Why

This directly addresses the issues raised in #1273 that were not fully solved by previous upstream commits. By isolating just these specific fixes on a fresh, synced branch off main, we avoid the "too many changed files" issue from previous PR attempts.

How to test

1. Checkout this branch.
2. Run pytest tests/test_e2e_api_suite.py - the test suite will now pass completely without failing during setup.
3. Run flake8 - no indentation or syntax errors will be reported for hybrid_model.py or celery_app.py.

Closes #1273

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[github-actions]

🎉 Welcome to Hybrid Recommender, @koushik-gupta! This is your first contribution here!

Labels added: gssoc:approved | mentor:leonagoel | status:review-needed

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