feat: implement GraphQL member management API

Implement complete member management system with GraphQL API per OpenSpec proposal.
Only firstName is required; all other fields are optional with conditional validation.

Key features:
- GraphQL CRUD operations (create, read, update, delete members)
- SQLAlchemy 2.0 async with SQLite database
- Alembic database migrations
- Conditional validation (email/phone validated only when provided)
- Member fields: firstName (required), lastName, address, email, phone (all optional)
- Database seed script with sample member
- FastAPI with Strawberry GraphQL integration

Implementation details:
- Python 3.11+ with uv package manager
- Async database sessions throughout
- Proper error handling and validation
- Code quality: black, isort, ruff
- Comprehensive end-to-end testing completed

All 20 tasks from OpenSpec proposal completed successfully.

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

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

src/models/__init__.py

@@ -0,0 +1,3 @@
+from src.models.member import Member
+
+__all__ = ["Member"]

src/models/member.py

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+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from src.database import Base
+
+
+class Member(Base):
+    """Member model for club/society management."""
+
+    __tablename__ = "members"
+
+    # Primary key
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+
+    # Required field
+    first_name: Mapped[str] = mapped_column(String(100), nullable=False)
+
+    # Optional fields
+    last_name: Mapped[Optional[str]] = mapped_column(String(100), nullable=True)
+    street: Mapped[Optional[str]] = mapped_column(String(200), nullable=True)
+    apartment_number: Mapped[Optional[str]] = mapped_column(String(20), nullable=True)
+    zip: Mapped[Optional[str]] = mapped_column(String(20), nullable=True)
+    city: Mapped[Optional[str]] = mapped_column(String(100), nullable=True)
+    country: Mapped[Optional[str]] = mapped_column(String(100), nullable=True)
+    email: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
+    phone: Mapped[Optional[str]] = mapped_column(String(50), nullable=True)
+
+    # Timestamps
+    created_at: Mapped[datetime] = mapped_column(
+        default=func.now(), server_default=func.now(), nullable=False
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        default=func.now(),
+        server_default=func.now(),
+        onupdate=func.now(),
+        nullable=False,
+    )
+
+    def __repr__(self) -> str:
+        return f"<Member(id={self.id}, first_name='{self.first_name}', last_name='{self.last_name}')>"