feat: SSH card UX, agent version sync, persistent ssh_admin_ok (0.11.5)

Silent SSH probe on host card open; manual test feedback auto-hides. Persist ssh_admin_ok in DB (migration 019). After agent update read version from host and refresh UI.

backend/alembic/versions/019_host_ssh_admin_status.py

@@ -0,0 +1,25 @@
+"""hosts: persist Linux SSH admin check status
+
+Revision ID: 019
+Revises: 018
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "019"
+down_revision: Union[str, None] = "018"
+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("ssh_admin_ok", sa.Boolean(), nullable=True))
+    op.add_column("hosts", sa.Column("ssh_admin_checked_at", sa.DateTime(timezone=True), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("hosts", "ssh_admin_checked_at")
+    op.drop_column("hosts", "ssh_admin_ok")