alerts: per-support-team webhook; printedparts routes low-stock to a chosen team

Support teams gain a webhookurl (migration 7d29 + API + settings-page field), so
a team is a notification target. send_webhook(url=) lets a caller override the
site default with a team's webhook. Printedparts gains a 'alert support team'
setting (printedparts_alert_supportteamid) + selector on its settings page;
low-stock alerts post to that team's webhook, falling back to the site
alert_webhook_url. Email leg unchanged. Same pattern extends to other alerting
plugins (printers low-toner next).

migrations/versions/7d29_supportteam_webhookurl.py

@@ -0,0 +1,41 @@
+"""Add supportteams.webhookurl (per-team alert webhook)
+
+A support team can carry a Teams (or other) webhook; alerting plugins route
+alerts to a team by selecting it. Nullable. Idempotent guard.
+
+Revision ID: 7d29_supportteam_webhookurl
+Revises: 7d28_dashboarddefault_displayrole
+Create Date: 2026-07-22
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = '7d29_supportteam_webhookurl'
+down_revision = '7d28_dashboarddefault_displayrole'
+branch_labels = None
+depends_on = None
+
+
+def _has_col(insp):
+    return any(c['name'] == 'webhookurl'
+               for c in insp.get_columns('supportteams'))
+
+
+def upgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'supportteams' not in insp.get_table_names():
+        return
+    if not _has_col(insp):
+        op.add_column('supportteams', sa.Column('webhookurl', sa.Text(), nullable=True))
+
+
+def downgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'supportteams' not in insp.get_table_names():
+        return
+    if _has_col(insp):
+        op.drop_column('supportteams', 'webhookurl')