feat: add Flask-Smorest OpenAPI configuration

[Shikha18Shukla]

🌸 Description

This PR adds the initial Swagger/OpenAPI configuration to the Flask backend using Flask-Smorest, laying the foundation for interactive API documentation without affecting existing application behavior.

Changes made:

• Added Flask-Smorest dependency to requirements.txt.
• Configured OpenAPI metadata:
  • API_TITLE
  • API_VERSION
  • OPENAPI_VERSION
• Configured Swagger UI endpoint at /docs.
• Initialized the Api object using Flask-Smorest.
• Added comments explaining the future migration from @app.route routes to Flask-Smorest Blueprints for automatic endpoint documentation.

The current backend routes continue to work as before. This change only establishes the OpenAPI infrastructure, making future API documentation easier to implement while keeping existing functionality unchanged.

Fixes #201

🛠️ Type of change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update (updating README, API docs, etc.)
• 💅 Styling (improving the UI/UX for a better user experience)

🔒 Privacy & Security (Crucial for Aarini)

• I have ensured that this change does NOT compromise user health data privacy.
• If this touches Firebase/Firestore, I have verified the security rules remain strict.

✅ Checklist:

• My code follows the style guidelines of this project (React Native / Flask).
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings (ESLint, Prettier, Python linters).
• I have added/updated tests where applicable.

🤝 ECSoC / ELUSOC 2026

• This PR is submitted under ECSoC / ELUSOC 2026.

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[Shikha18Shukla]

Hi @Him-an-shi, I've completed the implementation for #201 and opened this PR. I would appreciate it if you could review it when you have time. If there are any changes or improvements you'd like me to make, please let me know and I'll address them promptly. Otherwise, if everything looks good, I'd be grateful if you could merge it. Thank you! 😊