feat: add network_diagrams table

Create NetworkDiagram SQLAlchemy model with JSONB nodes/edges, team-scoped with client/asset metadata, and Alembic migration 074.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic/versions/074_add_network_diagrams_table.py

@@ -0,0 +1,41 @@
+"""Add network_diagrams table.
+
+Revision ID: 074
+Revises: 073
+Create Date: 2026-04-04
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+
+revision = "074"
+down_revision = "073"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "network_diagrams",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("team_id", UUID(as_uuid=True), sa.ForeignKey("teams.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("name", sa.String(255), nullable=False),
+        sa.Column("client_name", sa.String(255), nullable=True),
+        sa.Column("asset_name", sa.String(255), nullable=True),
+        sa.Column("description", sa.Text(), nullable=True),
+        sa.Column("nodes", JSONB(), nullable=False, server_default=sa.text("'[]'::jsonb")),
+        sa.Column("edges", JSONB(), nullable=False, server_default=sa.text("'[]'::jsonb")),
+        sa.Column("thumbnail_url", sa.Text(), nullable=True),
+        sa.Column("is_archived", sa.Boolean(), nullable=False, server_default=sa.text("false")),
+        sa.Column("created_by", UUID(as_uuid=True), sa.ForeignKey("users.id"), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.text("now()")),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.text("now()")),
+    )
+
+    op.create_index("idx_network_diagrams_team", "network_diagrams", ["team_id"])
+    op.create_index("idx_network_diagrams_client", "network_diagrams", ["team_id", "client_name"])
+
+
+def downgrade() -> None:
+    op.drop_table("network_diagrams")