feat: add patch generation for OSV dependency fixes

[Aharshi3614]

Linked issue

Closes #62

What this PR does

Adds patch generation for OSV dependency fixes.

Type of change

• Bug fix
• New feature
• ML model / training pipeline
• Refactor (no behaviour change)
• Documentation
• Tests only

ML tier (if applicable)

• Tier 1 — Triage
• Tier 2 — Predictive
• Tier 3 — Autonomous
• Not ML-related

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Changes

Backend

• Added patch_generator.py

Frontend

New dependencies

• None

Database / schema changes

• None

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Testing

How did you test this?
Ran locally with test requirements.txt file. Verified diff generation works.

Checklist

• Tested locally end-to-end (upload ZIP or GitHub URL → scan → findings returned correctly)
• New ML model falls back gracefully when model file is absent
• No new console.error or unhandled Python exceptions introduced
• Added or updated tests where applicable
• requirements.txt / package.json updated if new dependencies added
• New model files (.pkl, .pt, etc.) are gitignored, not committed

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Anything reviewers should focus on

None

Screenshots (if UI changed)

N/A

[github-actions]

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