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/enums.py

@@ -0,0 +1,123 @@
+# app/models/syndarix/enums.py
+"""
+Enums for Syndarix domain models.
+
+These enums represent the core state machines and categorizations
+used throughout the Syndarix AI consulting platform.
+"""
+
+from enum import Enum as PyEnum
+
+
+class AutonomyLevel(str, PyEnum):
+    """
+    Defines how much control the human has over agent actions.
+
+    FULL_CONTROL: Human must approve every agent action
+    MILESTONE: Human approves at sprint boundaries and major decisions
+    AUTONOMOUS: Agents work independently, only escalating critical issues
+    """
+
+    FULL_CONTROL = "full_control"
+    MILESTONE = "milestone"
+    AUTONOMOUS = "autonomous"
+
+
+class ProjectStatus(str, PyEnum):
+    """
+    Project lifecycle status.
+
+    ACTIVE: Project is actively being worked on
+    PAUSED: Project is temporarily on hold
+    COMPLETED: Project has been delivered successfully
+    ARCHIVED: Project is no longer accessible for work
+    """
+
+    ACTIVE = "active"
+    PAUSED = "paused"
+    COMPLETED = "completed"
+    ARCHIVED = "archived"
+
+
+class AgentStatus(str, PyEnum):
+    """
+    Current operational status of an agent instance.
+
+    IDLE: Agent is available but not currently working
+    WORKING: Agent is actively processing a task
+    WAITING: Agent is waiting for external input or approval
+    PAUSED: Agent has been manually paused
+    TERMINATED: Agent instance has been shut down
+    """
+
+    IDLE = "idle"
+    WORKING = "working"
+    WAITING = "waiting"
+    PAUSED = "paused"
+    TERMINATED = "terminated"
+
+
+class IssueStatus(str, PyEnum):
+    """
+    Issue workflow status.
+
+    OPEN: Issue is ready to be worked on
+    IN_PROGRESS: Agent or human is actively working on the issue
+    IN_REVIEW: Work is complete, awaiting review
+    BLOCKED: Issue cannot proceed due to dependencies or blockers
+    CLOSED: Issue has been completed or cancelled
+    """
+
+    OPEN = "open"
+    IN_PROGRESS = "in_progress"
+    IN_REVIEW = "in_review"
+    BLOCKED = "blocked"
+    CLOSED = "closed"
+
+
+class IssuePriority(str, PyEnum):
+    """
+    Issue priority levels.
+
+    LOW: Nice to have, can be deferred
+    MEDIUM: Standard priority, should be done
+    HIGH: Important, should be prioritized
+    CRITICAL: Must be done immediately, blocking other work
+    """
+
+    LOW = "low"
+    MEDIUM = "medium"
+    HIGH = "high"
+    CRITICAL = "critical"
+
+
+class SyncStatus(str, PyEnum):
+    """
+    External issue tracker synchronization status.
+
+    SYNCED: Local and remote are in sync
+    PENDING: Local changes waiting to be pushed
+    CONFLICT: Merge conflict between local and remote
+    ERROR: Synchronization failed due to an error
+    """
+
+    SYNCED = "synced"
+    PENDING = "pending"
+    CONFLICT = "conflict"
+    ERROR = "error"
+
+
+class SprintStatus(str, PyEnum):
+    """
+    Sprint lifecycle status.
+
+    PLANNED: Sprint has been created but not started
+    ACTIVE: Sprint is currently in progress
+    COMPLETED: Sprint has been finished successfully
+    CANCELLED: Sprint was cancelled before completion
+    """
+
+    PLANNED = "planned"
+    ACTIVE = "active"
+    COMPLETED = "completed"
+    CANCELLED = "cancelled"