Feat v0.3.2 workflow engine + handlers

Workflow execution engine with Start/Advance/Cancel lifecycle, automated
stage processor with Starlark hook firing and cycle guard (max 10),
instance and assignment HTTP handlers, store round-trip tests for all
v0.3.1 methods, and Starlark module expansion (get_instance, list_instances).

New routes:
- POST/GET /workflows/:id/instances (start, list)
- GET /workflows/:id/instances/:iid (get)
- POST /workflows/:id/instances/:iid/advance (advance)
- POST /workflows/:id/instances/:iid/cancel (cancel)
- POST /assignments/:id/claim|unclaim|complete|cancel
- GET /assignments/mine
- Team-scoped mirrors under /teams/:teamId/...

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/store/sqlite/workflows.go

@@ -633,6 +633,19 @@ func (s *WorkflowStore) ListAssignmentsByInstance(ctx context.Context, instanceI
 		ORDER BY created_at ASC`, instanceID)
 }
 
+func (s *WorkflowStore) ListAssignmentsByUser(ctx context.Context, userID string, status string) ([]models.WorkflowAssignment, error) {
+	q := `SELECT id, instance_id, stage, team_id, assigned_to, status,
+	             review_data, claimed_at, completed_at, created_at
+	      FROM workflow_assignments WHERE assigned_to = ?`
+	args := []interface{}{userID}
+	if status != "" {
+		q += " AND status = ?"
+		args = append(args, status)
+	}
+	q += " ORDER BY created_at DESC"
+	return s.queryAssignments(ctx, q, args...)
+}
+
 func (s *WorkflowStore) queryAssignments(ctx context.Context, q string, args ...interface{}) ([]models.WorkflowAssignment, error) {
 	rows, err := DB.QueryContext(ctx, q, args...)
 	if err != nil {