v0.172.0 fixup 2: drop import/* from the carry-list

Found on the demo-hp live leg: with import, import/paperless and import/calibre
in the carry-list, the derived skeleton RE-CREATES a per-drive drop-zone on every
drive forever — the dead lookalike the canonical root exists to remove, and one
that is never backed up (class: excluded).

Not a zero-removals violation: nothing deletes what an existing box has. Both
demo boxes' old drop-zones were verified to hold zero files before the change.

controller/internal/appbackup/skeleton_determinism_test.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"path/filepath"
 	"slices"
+	"strings"
 	"testing"
 )
 
@@ -132,3 +133,31 @@ func TestEnsureUserdataSkeletonCreatesOnly(t *testing.T) {
 		t.Errorf("a pre-existing customer dir was removed — zero-removals violated: %v", err)
 	}
 }
+
+// R-75: a DATA drive must never get a per-drive drop-zone from the skeleton. Carrying the old
+// `import/*` entries would have the skeleton re-create a dead lookalike on every drive forever —
+// one that is also never backed up, since import paths are class: excluded.
+//
+// This is NOT a zero-removals violation: nothing deletes the dirs a box already has (see
+// TestEnsureUserdataSkeletonCreatesOnly). They stop being maintained and stop appearing on fresh boxes.
+func TestSkeletonNeverCreatesAPerDriveDropZone(t *testing.T) {
+	// The catalog no longer implies any ${USERDATA_PATH}/import path — the binds moved to
+	// ${IMPORT_PATH} — so the only way one could appear is via the carry-list.
+	for _, derived := range [][]string{nil, {"media/podcasts", "roms"}} {
+		for _, d := range BuildUserdataSkeleton(derived) {
+			if d == "import" || strings.HasPrefix(d, "import/") {
+				t.Errorf("derived=%v: skeleton created a per-drive drop-zone %q — the canonical root is on the SYSTEM drive", derived, d)
+			}
+		}
+	}
+	for _, c := range UserdataSkeletonCarry() {
+		if c == "import" || strings.HasPrefix(c, "import/") {
+			t.Errorf("the carry-list still holds %q", c)
+		}
+	}
+	// A catalog app that genuinely declares a ${USERDATA_PATH}/import/... bind would still be
+	// honoured — the rule is "don't carry them", not "filter them out".
+	if !slices.Contains(BuildUserdataSkeleton([]string{"import/valami"}), "import/valami") {
+		t.Error("a genuinely derived userdata import path must still be created")
+	}
+}