feat: add is_admin column to users table

Add `is_admin` boolean column (default false) via Alembic migration
for role-based access control.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/alembic/versions/p7e8f9a0b1c2_add_is_admin_to_users.py

@@ -0,0 +1,29 @@
+"""add is_admin to users
+
+Revision ID: p7e8f9a0b1c2
+Revises: o6d7e8f9a0b1
+Create Date: 2026-03-21 10:00:00.000000
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "p7e8f9a0b1c2"
+down_revision: str | Sequence[str] | None = "o6d7e8f9a0b1"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "users",
+        sa.Column("is_admin", sa.Boolean(), nullable=False, server_default="false"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("users", "is_admin")

backend/src/app/models/user.py

@@ -4,7 +4,7 @@ from datetime import datetime
 from typing import TYPE_CHECKING
 from uuid import UUID
 
-from sqlalchemy import DateTime, String, func
+from sqlalchemy import Boolean, DateTime, String, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.core.database import Base
@@ -19,6 +19,7 @@ class User(Base):
     id: Mapped[UUID] = mapped_column(primary_key=True)
     email: Mapped[str] = mapped_column(String(255), unique=True, index=True)
     display_name: Mapped[str | None] = mapped_column(String(100))
+    is_admin: Mapped[bool] = mapped_column(Boolean, server_default="false")
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now()
     )