Feat/add insight generation route

[AAdewunmi]

Summary

Adds the authenticated insight generation route for study sessions.

Changes

• Added apps.insights.urls with the insights:generate route.
• Mounted insight routes under /insights/ in config/urls.py.
• Added GenerateInsightView for generating or reusing a session insight.
• Added permission tests for owner access, cross-user access, anonymous access, and POST-only behaviour.

Behaviour

• Route: /insights/sessions/<session_id>/generate/
• Named URL: insights:generate
• Only authenticated users can access it.
• Only the session owner can generate an insight.
• The route accepts POST only.
• GET returns 405.
• Cross-user access returns 404.
• Anonymous access redirects to login.
• Successful generation redirects back to the session detail page.

Why

This gives the UI a safe route for triggering insight generation while keeping permission checks and workflow logic behind the view/service boundary.

Validation

• python -m black . --check
• python -m ruff check .
• python -m pytest apps/insights/tests/test_insight_permissions.py -q
• python manage.py check --settings=config.settings.test

Result

Focused insight permission tests pass: 5 passed.

Notes

The route delegates generation to the insight service; the view does not import or run NLP helpers directly.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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