Add query preprocessing before hybrid retrieval

[Shalini828]

Summary

This PR introduces a query preprocessing step before hybrid retrieval.

Changes

• Added engine/preprocessing.py
• Implemented preprocess_query() to normalize user input
• Integrated preprocessing into search_pdfs() before retrieval logic

Why

This ensures consistent query formatting and improves retrieval quality by:

• Lowercasing queries
• Removing extra whitespace
• Standardizing input before embedding and keyword search

Impact

Improves robustness of hybrid search pipeline without affecting existing logic.

[github-actions]

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[SharanyaAchanta]

@Shalini828
Thanks for the PRs. I was away for a few days, so just catching up now.
There are some merge conflicts because of the recent updates. If you have some time, could you please resolve them according to the current architecture? Since we are approaching the project wrap-up,so we’ll need to wrap this up soon. If you're up for the challenge, go for it! All the best. If not, no worries at all thanks again for your contribution!

[Shalini828]

I've updated the PR according to the latest architecture and resolved the CI issues. All checks are now passing. Please let me know if anything else needs improvement.

[SharanyaAchanta]

Hi @Shalini828 Shalini, thanks for the update and for fixing the CI issues!

Just a heads-up: I merged another PR recently which caused some new conflicts in this branch. Since today is the final day of the program, I'm trying to wrap everything up quickly.

If you're able to resolve these new conflicts right away, please go ahead and I’ll check it. But if it’s taking too much time, no worries at all—you don't have to stress about it since we're on a tight deadline. Let me know what you think!

[SharanyaAchanta]

@Shalini828 Now the conflicts are resolved great job. But some checks failed please check that if you are free.

[Shalini828]

I've checked and the failing tests are resolved now. All checks are passing.

[SharanyaAchanta]

I've checked and the failing tests are resolved now. All checks are passing.

Great job Shalini

[SharanyaAchanta]

By the way @Shalini828 can you please link the issue number too.