feat(backend): Add Syndarix domain models with CRUD operations

- Add Project model with slug, description, autonomy level, and settings
- Add AgentType model for agent templates with model config and failover
- Add AgentInstance model for running agents with status and memory
- Add Issue model with external tracker sync (Gitea/GitHub/GitLab)
- Add Sprint model with velocity tracking and lifecycle management
- Add comprehensive Pydantic schemas with validation
- Add full CRUD operations for all models with filtering/sorting
- Add 280+ tests for models, schemas, and CRUD operations

Implements #23, #24, #25, #26, #27

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/models/syndarix/conftest.py

@@ -0,0 +1,192 @@
+# tests/models/syndarix/conftest.py
+"""
+Shared fixtures for Syndarix model tests.
+"""
+
+import uuid
+from datetime import date, timedelta
+
+import pytest
+import pytest_asyncio
+
+from app.models.syndarix import (
+    AgentInstance,
+    AgentStatus,
+    AgentType,
+    AutonomyLevel,
+    Issue,
+    IssuePriority,
+    IssueStatus,
+    Project,
+    ProjectStatus,
+    Sprint,
+    SprintStatus,
+    SyncStatus,
+)
+from app.models.user import User
+
+
+@pytest.fixture
+def sample_project_data():
+    """Return sample project data for testing."""
+    return {
+        "name": "Test Project",
+        "slug": "test-project",
+        "description": "A test project for unit testing",
+        "autonomy_level": AutonomyLevel.MILESTONE,
+        "status": ProjectStatus.ACTIVE,
+        "settings": {"mcp_servers": ["gitea", "slack"]},
+    }
+
+
+@pytest.fixture
+def sample_agent_type_data():
+    """Return sample agent type data for testing."""
+    return {
+        "name": "Backend Engineer",
+        "slug": "backend-engineer",
+        "description": "Specialized in backend development",
+        "expertise": ["python", "fastapi", "postgresql"],
+        "personality_prompt": "You are an expert backend engineer...",
+        "primary_model": "claude-opus-4-5-20251101",
+        "fallback_models": ["claude-sonnet-4-20250514"],
+        "model_params": {"temperature": 0.7, "max_tokens": 4096},
+        "mcp_servers": ["gitea", "file-system"],
+        "tool_permissions": {"allowed": ["*"], "denied": []},
+        "is_active": True,
+    }
+
+
+@pytest.fixture
+def sample_sprint_data():
+    """Return sample sprint data for testing."""
+    today = date.today()
+    return {
+        "name": "Sprint 1",
+        "number": 1,
+        "goal": "Complete initial setup and core features",
+        "start_date": today,
+        "end_date": today + timedelta(days=14),
+        "status": SprintStatus.PLANNED,
+        "planned_points": 21,
+        "completed_points": 0,
+    }
+
+
+@pytest.fixture
+def sample_issue_data():
+    """Return sample issue data for testing."""
+    return {
+        "title": "Implement user authentication",
+        "body": "As a user, I want to log in securely...",
+        "status": IssueStatus.OPEN,
+        "priority": IssuePriority.HIGH,
+        "labels": ["backend", "security"],
+        "story_points": 5,
+    }
+
+
+@pytest_asyncio.fixture
+async def test_owner(async_test_db):
+    """Create a test user to be used as project owner."""
+    from app.core.auth import get_password_hash
+
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        user = User(
+            id=uuid.uuid4(),
+            email="owner@example.com",
+            password_hash=get_password_hash("TestPassword123!"),
+            first_name="Test",
+            last_name="Owner",
+            is_active=True,
+            is_superuser=False,
+        )
+        session.add(user)
+        await session.commit()
+        await session.refresh(user)
+        return user
+
+
+@pytest_asyncio.fixture
+async def test_project(async_test_db, test_owner, sample_project_data):
+    """Create a test project in the database."""
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        project = Project(
+            id=uuid.uuid4(),
+            owner_id=test_owner.id,
+            **sample_project_data,
+        )
+        session.add(project)
+        await session.commit()
+        await session.refresh(project)
+        return project
+
+
+@pytest_asyncio.fixture
+async def test_agent_type(async_test_db, sample_agent_type_data):
+    """Create a test agent type in the database."""
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        agent_type = AgentType(
+            id=uuid.uuid4(),
+            **sample_agent_type_data,
+        )
+        session.add(agent_type)
+        await session.commit()
+        await session.refresh(agent_type)
+        return agent_type
+
+
+@pytest_asyncio.fixture
+async def test_agent_instance(async_test_db, test_project, test_agent_type):
+    """Create a test agent instance in the database."""
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        agent_instance = AgentInstance(
+            id=uuid.uuid4(),
+            agent_type_id=test_agent_type.id,
+            project_id=test_project.id,
+            status=AgentStatus.IDLE,
+            current_task=None,
+            short_term_memory={},
+            long_term_memory_ref=None,
+            session_id=None,
+        )
+        session.add(agent_instance)
+        await session.commit()
+        await session.refresh(agent_instance)
+        return agent_instance
+
+
+@pytest_asyncio.fixture
+async def test_sprint(async_test_db, test_project, sample_sprint_data):
+    """Create a test sprint in the database."""
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        sprint = Sprint(
+            id=uuid.uuid4(),
+            project_id=test_project.id,
+            **sample_sprint_data,
+        )
+        session.add(sprint)
+        await session.commit()
+        await session.refresh(sprint)
+        return sprint
+
+
+@pytest_asyncio.fixture
+async def test_issue(async_test_db, test_project, sample_issue_data):
+    """Create a test issue in the database."""
+    _test_engine, AsyncTestingSessionLocal = async_test_db
+    async with AsyncTestingSessionLocal() as session:
+        issue = Issue(
+            id=uuid.uuid4(),
+            project_id=test_project.id,
+            **sample_issue_data,
+        )
+        session.add(issue)
+        await session.commit()
+        await session.refresh(issue)
+        return issue