feat(project): add Project entity and ProjectRepository interface

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/modules/project/domain/entities.py

@@ -0,0 +1,11 @@
+from dataclasses import dataclass
+from datetime import datetime
+
+
+@dataclass
+class Project:
+    id: str
+    name: str
+    design_dir: str
+    code_dir: str | None
+    created_at: datetime

backend/app/modules/project/domain/repositories.py

@@ -0,0 +1,21 @@
+from abc import ABC, abstractmethod
+
+from app.modules.project.domain.entities import Project
+
+
+class ProjectRepository(ABC):
+    @abstractmethod
+    def list_all(self) -> list[Project]:
+        ...
+
+    @abstractmethod
+    def get_by_id(self, project_id: str) -> Project | None:
+        ...
+
+    @abstractmethod
+    def save(self, project: Project) -> None:
+        ...
+
+    @abstractmethod
+    def delete(self, project_id: str) -> None:
+        ...