chore: pin requirements + pnpm deps

[inimaz]

Description

Continuation of #1294 .

This PR:

• pins pre-commit steps
• pins requirements-api.txt
• updates Docker image of the webapp so that it depends on the pnpm version of the package.json

AI Usage Disclosure

Please refer to docs/how-to/ai-policy.md for detailed guidelines on how to disclose AI usage in your PR. Accurately completing this section is mandatory.

• 🟥 AI-vibecoded: You cannot explain the logic. Car analogy : the car drive by itself, you are outside it and just tell it where to go.
• 🟠 AI-generated: Car analogy : the car drive by itself, you are inside and give instructions.
• ⭐ AI-assisted. Car analogy : you drive the car, AI help you find your way.
• ♻️ No AI used. Car analogy : you drive the car.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.43%. Comparing base (3287221) to head (1a57c51).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1295   +/-   ##
=======================================
  Coverage   91.43%   91.43%           
=======================================
  Files          49       49           
  Lines        5056     5056           
=======================================
  Hits         4623     4623           
  Misses        433      433           

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