v0.172.0 — R-75: canonical import root, catalog-derived skeleton, import surfaces

${IMPORT_PATH} = <system namespace root>/userdata/import — ONE drop-zone per box,
on the system drive, injected at BOTH compose-env builders with NO per-drive
fallback (unresolvable leaves it unset so compose fails loudly rather than
quietly building a second, dead drop-zone).

Third BindRoot (RootImport) + Import list in BackupSpec, extended through
ValidateBackupSpec/ClassifyBinds. Load-bearing: a stale `userdata: import/<app>`
entry against the moved bind would be a WHOLE-BLOCK reject, taking the app's
mandatory hdd classification with it.

Exhaustive-root audit: resolveAbs/structuralGuard/ComputeCaptureSet/
ComputeFabBuckets now take importRoot explicitly (an import bind resolved
against hddPath would name a directory on the wrong drive); unresolvable is
refused loudly into Skipped. GetImportRoot added to both provider interfaces.

Catalog-derived skeleton: UserdataSkeleton() -> UserdataSkeletonCarry() +
BuildUserdataSkeleton(), SORTED. The carry-list makes zero-removals true by
construction (`documents` is in no catalog app but on both boxes) and is the
fresh-box floor. The sort is not tidiness: the naive map-order derivation
measured 20 distinct outputs from 20 identical runs, which with fbNeedsRecreate
is a fleet-wide FileBrowser restart loop.

One authoritative compose parser: ParseComposeUserdataMounts now delegates to
ParseComposeClassifiableBinds. Import root excluded from per-app migration.

Surfaces: FileBrowser /srv/beolvasas source; app-page "Hova tegyem a fajlokat?"
with PathEscape deep links (never QueryEscape) and class-driven copy;
data_paths: annotation with the Fork-3 asymmetry; system-owned beolvasas SMB
share refused server-side at handler AND store, button omitted in template.

Caught on the way: the sharing template's row struct was function-local, so
adding {{if .System}} would have 500'd every share row. ShareRow is now
package-level and the render test uses the handler's own type.

Tests 915 -> 949, all green. MinAgent unchanged.

controller/internal/appbackup/userdata_test.go

@@ -13,10 +13,12 @@ func TestSharedContentGID(t *testing.T) {
 	}
 }
 
-// TestUserdataSkeleton_List asserts the locked skeleton subdir set.
+// TestUserdataSkeleton_List asserts the locked skeleton subdir set. R-75 renamed the hardcoded list
+// to UserdataSkeletonCarry (it is now the non-derived carry-list); the asserted set is UNCHANGED,
+// which is exactly the zero-removals promise.
 func TestUserdataSkeleton_List(t *testing.T) {
 	got := map[string]bool{}
-	for _, s := range UserdataSkeleton() {
+	for _, s := range UserdataSkeletonCarry() {
 		got[s] = true
 	}
 	for _, want := range []string{
@@ -41,9 +43,10 @@ func TestUserdataDir(t *testing.T) {
 // is ignored — dirs + setgid still land). Runs cross-platform.
 func TestEnsureUserdataSkeleton_Structure(t *testing.T) {
 	ns := t.TempDir()
-	_ = EnsureUserdataSkeleton(ns) // ignore chown error on a non-root CI host
+	dirs := BuildUserdataSkeleton(nil)   // no catalog derived → the carry-list floor
+	_ = EnsureUserdataSkeleton(ns, dirs) // ignore chown error on a non-root CI host
 	base := UserdataDir(ns)
-	for _, sub := range append([]string{""}, UserdataSkeleton()...) {
+	for _, sub := range append([]string{""}, dirs...) {
 		p := filepath.Join(base, sub)
 		if fi, err := os.Stat(p); err != nil || !fi.IsDir() {
 			t.Errorf("skeleton dir missing: %s (%v)", p, err)