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/app/models/syndarix/project.py

@@ -0,0 +1,88 @@
+# app/models/syndarix/project.py
+"""
+Project model for Syndarix AI consulting platform.
+
+A Project represents a client engagement where AI agents collaborate
+to deliver software solutions.
+"""
+
+from sqlalchemy import Column, Enum, ForeignKey, Index, String, Text
+from sqlalchemy.dialects.postgresql import (
+    JSONB,
+    UUID as PGUUID,
+)
+from sqlalchemy.orm import relationship
+
+from app.models.base import Base, TimestampMixin, UUIDMixin
+
+from .enums import AutonomyLevel, ProjectStatus
+
+
+class Project(Base, UUIDMixin, TimestampMixin):
+    """
+    Project model representing a client engagement.
+
+    A project contains:
+    - Configuration for how autonomous agents should operate
+    - Settings for MCP server integrations
+    - Relationship to assigned agents, issues, and sprints
+    """
+
+    __tablename__ = "projects"
+
+    name = Column(String(255), nullable=False, index=True)
+    slug = Column(String(255), unique=True, nullable=False, index=True)
+    description = Column(Text, nullable=True)
+
+    autonomy_level: Column[AutonomyLevel] = Column(
+        Enum(AutonomyLevel),
+        default=AutonomyLevel.MILESTONE,
+        nullable=False,
+        index=True,
+    )
+
+    status: Column[ProjectStatus] = Column(
+        Enum(ProjectStatus),
+        default=ProjectStatus.ACTIVE,
+        nullable=False,
+        index=True,
+    )
+
+    # JSON field for flexible project configuration
+    # Can include: mcp_servers, webhook_urls, notification_settings, etc.
+    settings = Column(JSONB, default=dict, nullable=False)
+
+    # Foreign key to the User who owns this project
+    owner_id = Column(
+        PGUUID(as_uuid=True),
+        ForeignKey("users.id", ondelete="SET NULL"),
+        nullable=True,
+        index=True,
+    )
+
+    # Relationships
+    owner = relationship("User", foreign_keys=[owner_id])
+    agent_instances = relationship(
+        "AgentInstance",
+        back_populates="project",
+        cascade="all, delete-orphan",
+    )
+    issues = relationship(
+        "Issue",
+        back_populates="project",
+        cascade="all, delete-orphan",
+    )
+    sprints = relationship(
+        "Sprint",
+        back_populates="project",
+        cascade="all, delete-orphan",
+    )
+
+    __table_args__ = (
+        Index("ix_projects_slug_status", "slug", "status"),
+        Index("ix_projects_owner_status", "owner_id", "status"),
+        Index("ix_projects_autonomy_status", "autonomy_level", "status"),
+    )
+
+    def __repr__(self) -> str:
+        return f"<Project {self.name} ({self.slug}) status={self.status.value}>"