Implement Phase 3: dynamic graph builder, blueprint persistence, and CRUD API

- Add dynamic_graph_builder.py that constructs LangGraph graphs at runtime
  from frontend CouncilBlueprint JSON (no more hardcoded graphs in production)
- Add PostgreSQL persistence via SQLAlchemy async with Blueprint model
- Add blueprint CRUD endpoints (POST/GET/PUT/DELETE /api/councils/)
- Add POST /api/councils/{id}/run to execute blueprints dynamically
- Add Alembic migration infrastructure with initial blueprints table
- Add database.py with async engine and SQLite fallback for dev/test
- Fix missing typing-extensions and add aiosqlite dependency
- Add 42 new tests (80/80 total passing) covering dynamic graph building,
  blueprint service CRUD, and API integration

https://claude.ai/code/session_014yZUxrPsgZbvkebXbCXR4U

backend/models/blueprint.py

@@ -0,0 +1,62 @@
+"""
+Blueprint model — stores council blueprints as JSON in PostgreSQL.
+
+Each blueprint represents a complete council graph configuration created
+by the user in the "Rat-Architekt" (Setup Mode) frontend tab.
+"""
+
+import uuid
+from datetime import datetime, timezone
+
+from sqlalchemy import Column, DateTime, Integer, JSON, String
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    """SQLAlchemy declarative base for all models."""
+
+    pass
+
+
+class Blueprint(Base):
+    """
+    A council blueprint stored in PostgreSQL.
+
+    The nodes and edges are stored as JSON columns matching the
+    CouncilBlueprint TypeScript interface from the frontend.
+    """
+
+    __tablename__ = "blueprints"
+
+    id = Column(
+        String(36),
+        primary_key=True,
+        default=lambda: str(uuid.uuid4()),
+    )
+    version = Column(Integer, nullable=False, default=1)
+    name = Column(String(255), nullable=False)
+    nodes = Column(JSON, nullable=False, default=list)
+    edges = Column(JSON, nullable=False, default=list)
+    created_at = Column(
+        DateTime(timezone=True),
+        nullable=False,
+        default=lambda: datetime.now(timezone.utc),
+    )
+    updated_at = Column(
+        DateTime(timezone=True),
+        nullable=False,
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc),
+    )
+
+    def to_dict(self) -> dict:
+        """Serialize to the CouncilBlueprint JSON format expected by the frontend."""
+        return {
+            "id": self.id,
+            "version": self.version,
+            "name": self.name,
+            "nodes": self.nodes,
+            "edges": self.edges,
+            "createdAt": self.created_at.isoformat() if self.created_at else None,
+            "updatedAt": self.updated_at.isoformat() if self.updated_at else None,
+        }