Give every notification type its own row on the board

The shopfloor board grouped cards by display style alone, so every type set to
grid landed inside the Recertification row and every carousel type inside
Recognition's - under a heading naming somebody else's type. Setting Awareness
to grid put awareness messages under "Recertification Required".

Each type now gets a row of its own, titled by its own name, and rotation state
is per row: two carousel rows advance on their own indexes instead of sharing
one counter, and two grid rows page independently.

For the other direction there is notificationtypes.boardcategory. Types sharing
a category share one row under the category name, so Change, Awareness and
Incident can sit together while Recognition and Recertification keep their own.
Blank - the default - means a row of its own. The category is part of the
grouping key along with the display style, since a category cannot merge a
banner with a row of tiles.

A card that names no employee now renders its message as the tile or card,
rather than a placeholder face above a blank name, which is what a grid type
like Awareness looked like before.

The layout fingerprint that makes open kiosks reload now covers the category
and the grace window, so a re-grouped board reaches screens that are already up.

plugins/notifications/migrations/versions/0004_boardcategory.py

@@ -0,0 +1,47 @@
+"""Add notificationtypes.boardcategory (shared heading on the shopfloor board).
+
+The board grouped cards by display style alone, so every type set to grid landed
+inside the Recertification row and every carousel type inside Recognition's,
+under a heading that named someone else's type. Each type now gets a row of its
+own; this column is the opt-in for the other direction - several types that
+belong together (Change, Awareness, Incident) share one row under a category
+name instead of taking three.
+
+Idempotent; downgrade drops the column.
+
+Revision ID: notifications0004category
+Revises: notifications0003grace
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = 'notifications0004category'
+down_revision = 'notifications0003grace'
+branch_labels = None
+depends_on = None
+
+_TABLE = 'notificationtypes'
+_COLUMN = 'boardcategory'
+
+
+def _column_names(insp, table):
+    return {c['name'] for c in insp.get_columns(table)}
+
+
+def upgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if _TABLE not in insp.get_table_names():
+        return
+    if _COLUMN not in _column_names(insp, _TABLE):
+        op.add_column(_TABLE, sa.Column(_COLUMN, sa.String(50), nullable=True))
+
+
+def downgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if _TABLE not in insp.get_table_names():
+        return
+    if _COLUMN in _column_names(insp, _TABLE):
+        op.drop_column(_TABLE, _COLUMN)