feat: Implement domain logic separation with clean architecture

- Created complete domain layer with pure business logic
- Implemented Issue domain models with 48 passing tests
- Implemented Project domain models with 31 passing tests
- Added domain services for complex business operations
- Established clean separation between domain, application, and infrastructure
- All 250 tests passing with no breaking changes

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

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

domain/issues/models.py

@@ -0,0 +1,116 @@
+"""
+Issue domain models.
+
+Contains core business entities and value objects for issue management.
+"""
+
+from dataclasses import dataclass
+from typing import List, Optional
+from datetime import datetime
+from enum import Enum
+
+from .exceptions import IssueStateError
+
+
+class IssueState(Enum):
+    """Issue state enumeration."""
+    OPEN = "open"
+    CLOSED = "closed"
+    IN_PROGRESS = "in_progress"
+
+
+@dataclass(frozen=True)
+class Label:
+    """Value object representing an issue label."""
+    name: str
+    color: Optional[str] = None
+    description: Optional[str] = None
+
+    def is_state_label(self) -> bool:
+        """Check if this is a state-related label."""
+        return self.name.startswith('status:')
+
+    def is_priority_label(self) -> bool:
+        """Check if this is a priority-related label."""
+        return self.name.startswith('priority:')
+
+    def is_type_label(self) -> bool:
+        """Check if this is a type-related label."""
+        return self.name in ['bug', 'enhancement', 'feature', 'documentation']
+
+
+@dataclass(frozen=True)
+class LabelCategories:
+    """Value object for categorized labels."""
+    state_labels: List[str]
+    priority_labels: List[str]
+    type_labels: List[str]
+    other_labels: List[str]
+
+
+@dataclass
+class Issue:
+    """Issue aggregate root."""
+    number: int
+    title: str
+    state: IssueState
+    labels: List[Label]
+    created_at: datetime
+    updated_at: datetime
+    milestone: Optional[str] = None
+    assignee: Optional[str] = None
+    closed_at: Optional[datetime] = None
+
+    def categorize_labels(self) -> LabelCategories:
+        """Categorize labels by type - pure domain logic."""
+        state_labels = [label.name for label in self.labels if label.is_state_label()]
+        priority_labels = [label.name for label in self.labels if label.is_priority_label()]
+        type_labels = [label.name for label in self.labels if label.is_type_label()]
+        other_labels = [
+            label.name for label in self.labels
+            if not (label.is_state_label() or label.is_priority_label() or label.is_type_label())
+        ]
+
+        return LabelCategories(
+            state_labels=state_labels,
+            priority_labels=priority_labels,
+            type_labels=type_labels,
+            other_labels=other_labels
+        )
+
+    def close(self) -> None:
+        """Close the issue - domain business rule."""
+        if self.state == IssueState.CLOSED:
+            raise IssueStateError(
+                "Issue is already closed",
+                current_state=self.state.value,
+                attempted_state=IssueState.CLOSED.value
+            )
+
+        self.state = IssueState.CLOSED
+        self.closed_at = datetime.utcnow()
+
+    def reopen(self) -> None:
+        """Reopen the issue - domain business rule."""
+        if self.state != IssueState.CLOSED:
+            raise IssueStateError(
+                "Issue is not closed",
+                current_state=self.state.value,
+                attempted_state=IssueState.OPEN.value
+            )
+
+        self.state = IssueState.OPEN
+        self.closed_at = None
+
+    def add_label(self, label: Label) -> None:
+        """Add a label to the issue."""
+        if label not in self.labels:
+            self.labels.append(label)
+
+    def remove_label(self, label_name: str) -> None:
+        """Remove a label from the issue."""
+        self.labels = [label for label in self.labels if label.name != label_name]
+
+    def has_label(self, label_name: str) -> bool:
+        """Check if issue has a specific label."""
+        return any(label.name == label_name for label in self.labels)