feat(fase4): add FlowTemplate model and API

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/api-gateway/app/models/flow_template.py

@@ -0,0 +1,21 @@
+import uuid
+from datetime import datetime
+from sqlalchemy import Column, String, Text, DateTime, Boolean, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from app.core.database import Base
+
+
+class FlowTemplate(Base):
+    __tablename__ = "flow_templates"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String(100), nullable=False)
+    description = Column(Text, nullable=True)
+    category = Column(String(50), default="general", nullable=False)
+    nodes = Column(JSONB, default=list)
+    edges = Column(JSONB, default=list)
+    variables = Column(JSONB, default=dict)
+    preview_image = Column(String(500), nullable=True)
+    is_public = Column(Boolean, default=True, nullable=False)
+    created_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)