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/schemas/syndarix/project.py

@@ -0,0 +1,127 @@
+# app/schemas/syndarix/project.py
+"""
+Pydantic schemas for Project entity.
+"""
+
+import re
+from datetime import datetime
+from typing import Any
+from uuid import UUID
+
+from pydantic import BaseModel, ConfigDict, Field, field_validator
+
+from .enums import AutonomyLevel, ProjectStatus
+
+
+class ProjectBase(BaseModel):
+    """Base project schema with common fields."""
+
+    name: str = Field(..., min_length=1, max_length=255)
+    slug: str | None = Field(None, min_length=1, max_length=255)
+    description: str | None = None
+    autonomy_level: AutonomyLevel = AutonomyLevel.MILESTONE
+    status: ProjectStatus = ProjectStatus.ACTIVE
+    settings: dict[str, Any] = Field(default_factory=dict)
+
+    @field_validator("slug")
+    @classmethod
+    def validate_slug(cls, v: str | None) -> str | None:
+        """Validate slug format: lowercase, alphanumeric, hyphens only."""
+        if v is None:
+            return v
+        if not re.match(r"^[a-z0-9-]+$", v):
+            raise ValueError(
+                "Slug must contain only lowercase letters, numbers, and hyphens"
+            )
+        if v.startswith("-") or v.endswith("-"):
+            raise ValueError("Slug cannot start or end with a hyphen")
+        if "--" in v:
+            raise ValueError("Slug cannot contain consecutive hyphens")
+        return v
+
+    @field_validator("name")
+    @classmethod
+    def validate_name(cls, v: str) -> str:
+        """Validate project name."""
+        if not v or v.strip() == "":
+            raise ValueError("Project name cannot be empty")
+        return v.strip()
+
+
+class ProjectCreate(ProjectBase):
+    """Schema for creating a new project."""
+
+    name: str = Field(..., min_length=1, max_length=255)
+    slug: str = Field(..., min_length=1, max_length=255)
+    owner_id: UUID | None = None
+
+
+class ProjectUpdate(BaseModel):
+    """Schema for updating a project."""
+
+    name: str | None = Field(None, min_length=1, max_length=255)
+    slug: str | None = Field(None, min_length=1, max_length=255)
+    description: str | None = None
+    autonomy_level: AutonomyLevel | None = None
+    status: ProjectStatus | None = None
+    settings: dict[str, Any] | None = None
+    owner_id: UUID | None = None
+
+    @field_validator("slug")
+    @classmethod
+    def validate_slug(cls, v: str | None) -> str | None:
+        """Validate slug format."""
+        if v is None:
+            return v
+        if not re.match(r"^[a-z0-9-]+$", v):
+            raise ValueError(
+                "Slug must contain only lowercase letters, numbers, and hyphens"
+            )
+        if v.startswith("-") or v.endswith("-"):
+            raise ValueError("Slug cannot start or end with a hyphen")
+        if "--" in v:
+            raise ValueError("Slug cannot contain consecutive hyphens")
+        return v
+
+    @field_validator("name")
+    @classmethod
+    def validate_name(cls, v: str | None) -> str | None:
+        """Validate project name."""
+        if v is not None and (not v or v.strip() == ""):
+            raise ValueError("Project name cannot be empty")
+        return v.strip() if v else v
+
+
+class ProjectInDB(ProjectBase):
+    """Schema for project in database."""
+
+    id: UUID
+    owner_id: UUID | None = None
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class ProjectResponse(ProjectBase):
+    """Schema for project API responses."""
+
+    id: UUID
+    owner_id: UUID | None = None
+    created_at: datetime
+    updated_at: datetime
+    agent_count: int | None = 0
+    issue_count: int | None = 0
+    active_sprint_name: str | None = None
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class ProjectListResponse(BaseModel):
+    """Schema for paginated project list responses."""
+
+    projects: list[ProjectResponse]
+    total: int
+    page: int
+    page_size: int
+    pages: int