Add customizable email templates and remove alert recipients

Replaced the fixed `alert_recipients` list with customizable subject and body templates for alerts and warnings. This allows for more flexible and dynamic email notifications using placeholder variables. Updated relevant backend and frontend components to support this feature.

backend/alembic/versions/0007_email_templates.py

@@ -0,0 +1,31 @@
+"""email templates and drop recipients list
+
+Revision ID: 0007_email_templates
+Revises: 0006_email_from_name
+Create Date: 2026-02-12
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0007_email_templates"
+down_revision = "0006_email_from_name"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("email_notification_settings", sa.Column("warning_subject_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("alert_subject_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("warning_body_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("alert_body_template", sa.Text(), nullable=True))
+    op.drop_column("email_notification_settings", "alert_recipients")
+
+
+def downgrade() -> None:
+    op.add_column("email_notification_settings", sa.Column("alert_recipients", sa.JSON(), nullable=False, server_default="[]"))
+    op.drop_column("email_notification_settings", "alert_body_template")
+    op.drop_column("email_notification_settings", "warning_body_template")
+    op.drop_column("email_notification_settings", "alert_subject_template")
+    op.drop_column("email_notification_settings", "warning_subject_template")