Initial commit: CLEAN architecture foundation for fantasy hockey backend

Implemented CLEAN architecture with clear separation of concerns:
- Domain layer with entities (Player, Team, Stats, FantasyTeam) and repository interfaces
- Application layer with use case implementations
- Infrastructure layer with NHL API and Yahoo Fantasy API adapters
- Presentation layer with FastAPI configuration and dependency injection

Key features:
- Swappable data source adapters (NHL API, Yahoo Fantasy API)
- Repository pattern for data access abstraction
- Dependency injection for loose coupling
- FastAPI framework with async support
- PostgreSQL database configuration
- Environment-based configuration management

Technology stack: Python 3.11+, FastAPI, PostgreSQL, nhl-api-py, yfpy

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

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

src/domain/repositories/team_repository.py

@@ -0,0 +1,29 @@
+"""Team repository interface."""
+from abc import ABC, abstractmethod
+from typing import List, Optional
+
+from src.domain.entities import NHLTeam
+
+
+class TeamRepository(ABC):
+    """Abstract interface for NHL team data access."""
+
+    @abstractmethod
+    async def get_team_by_id(self, team_id: str) -> Optional[NHLTeam]:
+        """Retrieves a team by its unique identifier."""
+        pass
+
+    @abstractmethod
+    async def get_all_teams(self) -> List[NHLTeam]:
+        """Retrieves all NHL teams."""
+        pass
+
+    @abstractmethod
+    async def get_teams_by_division(self, division: str) -> List[NHLTeam]:
+        """Retrieves all teams in a specific division."""
+        pass
+
+    @abstractmethod
+    async def get_teams_by_conference(self, conference: str) -> List[NHLTeam]:
+        """Retrieves all teams in a specific conference."""
+        pass