Add comprehensive edge-case tests for AI Parenting feature

[devin-ai-integration]

Summary

Adds 185 edge-case tests across 8 test files for the AI Parenting Guide backend (apps/ai-parenting-guide/backend/tests/). Covers:

Test file	Tests	Focus
test_gemini_ai_service.py	38	Boundary values, empty inputs, cache hit/miss, model errors, concurrent requests, helper methods
test_auth_service.py	23	Password hashing (empty, unicode, bcrypt boundary), JWT creation/decoding, token blacklisting, auth flows
test_rate_limiter.py	21	Role-based limits, boundary values, burst detection, Redis fail-open, concurrent users, admin reset
test_api_endpoints.py	24	Input validation (min/max), empty bodies, service error 500s, health checks, community CRUD
test_schemas.py	35	Pydantic validation boundaries, required fields, enum validation, points range, duration constraints
test_middleware.py	8	Security headers, endpoint type detection, public endpoint bypass, request logging
test_models.py	16	User/Discussion/Comment creation, unique constraints, cascade deletes, default values
test_file_upload.py	10	Upload stub, multimodal analysis (image/text/mixed), large content, concurrent analysis

Also includes conftest.py with compatibility patches for existing code issues discovered during testing:

• Pydantic v2 regex → pattern migration needed in schemas/learning.py
• Base import mismatch in models/learning.py
• AuthService.require_role async factory issue
• UserSession.token_jti vs UserSession.token mismatch
• Missing schema stubs (UserUpdate, etc.)

All 185 tests pass locally: pytest tests/ -v ✓

Review & Testing Checklist for Human

• Run cd apps/ai-parenting-guide/backend && pip install -r requirements.txt && pip install pytest pytest-asyncio httpx && pytest tests/ -v to verify all tests pass
• Review conftest.py compatibility patches — these workaround existing code bugs that should be addressed separately
• Verify test coverage is adequate for your risk tolerance (run with --cov=app for coverage report)

Notes

• The existing codebase has several compatibility issues (pydantic v2 migration incomplete, model/service mismatches) — these are noted in the conftest but NOT fixed in this PR to keep scope focused on tests only.
• bcrypt 4.0.1 is needed (bcrypt 5.x rejects passwords in passlib's internal detection code)

Link to Devin session: https://app.devin.ai/sessions/7af5954fecba4ab78cb8d603a076ab43
Requested by: @sakomws

[devin-ai-integration]

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