feat(database): add llm_setup_completed_at column to workspaces for onboarding tracking

surfsense_backend/alembic/versions/174_add_llm_setup_completed_at.py

@@ -0,0 +1,30 @@
+"""Add workspaces.llm_setup_completed_at for first-run vs. recovery onboarding.
+
+No backfill: NULL is correct for every existing row. Configured workspaces
+self-heal via lazy stamping on their next status read (which fires while still
+``ready``, before they could reach ``needs_setup``); a blanket
+``SET ... = created_at`` would misclassify abandoned and global-only workspaces.
+
+Revision ID: 174
+Revises: 173
+"""
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "174"
+down_revision: str | None = "173"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute(
+        "ALTER TABLE workspaces "
+        "ADD COLUMN IF NOT EXISTS llm_setup_completed_at TIMESTAMPTZ"
+    )
+
+
+def downgrade() -> None:
+    op.execute("ALTER TABLE workspaces DROP COLUMN IF EXISTS llm_setup_completed_at")