[Database] Implement async CRUD operations for core entities (incidents, model registry, policy audits)

[saviornt]

Description

Implement reusable, type-safe, async CRUD operations for the main entities so both Appliance and Assistant can safely read/write without duplicating logic.

Type

• Task

Focus Area (pick one)

• Shared Utils & Models

Priority

• Medium

Acceptance Criteria

• File: shared/src/database/crud.py
• Async CRUD operations for:
  • Incidents: create, get_by_id, get_recent, get_by_device_mac, mark_resolved
  • ModelRegistry: create_new_version, get_latest, get_by_hash, list_versions
  • PolicyAudits: log_action, get_for_incident
• All functions accept AsyncSession from session.py
• Use SQLAlchemy 2.0 select() / insert() / update() style
• Return Pydantic models via .model_validate(db_obj)
• Basic filtering + pagination (limit / offset)
• Proper exception handling (custom NotFoundError, DuplicateError, etc.)
• Unit tests covering happy path + edge cases (no results, constraint violations)
• Full Google-style docstrings
• Type annotations; mypy strict clean

Blocker / Dependencies

• [Database] Implement robust async SQLite session factory + connection pooling
• [Database] Define Pydantic v2 models and initial relational schema

Notes / Links

• Related files: shared/src/database/schemas.py, shared/src/database/models.py