feat: host inventory (agent.inventory), host detail page, UI columns

Store hardware/software snapshots on hosts; warn on hardware changes. Host card from Hosts list. Add agent version column to Events/Overview; rename Hosts table columns and sort by status.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/alembic/versions/013_host_inventory.py

@@ -0,0 +1,26 @@
+"""host inventory JSONB
+
+Revision ID: 013
+Revises: 012
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects.postgresql import JSONB
+
+revision: str = "013"
+down_revision: Union[str, None] = "012"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("hosts", sa.Column("inventory", JSONB, nullable=True))
+    op.add_column("hosts", sa.Column("inventory_updated_at", sa.DateTime(timezone=True), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("hosts", "inventory_updated_at")
+    op.drop_column("hosts", "inventory")