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/web/templates/app_info.html

@@ -71,6 +71,24 @@
          onerror="this.style.display='none'">
 </div>
 
+{{if .DataPathCards}}
+<div class="app-info-card" style="margin-top:1rem">
+    <h3>Hova tegyem a fájlokat?</h3>
+    <p class="form-hint">Ezeket a mappákat a Fájlkezelőben éred el. Előfordulhat, hogy először be kell jelentkezned a Fájlkezelőbe.</p>
+    <div class="datapath-list">
+        {{range .DataPathCards}}
+        <div class="datapath-row">
+            <div class="datapath-head">
+                <a href="{{.Link}}" target="_blank" rel="noopener" class="datapath-link">{{.Label}} ↗</a>
+                {{if .FreeSpace}}<span class="datapath-space">{{.FreeSpace}}</span>{{end}}
+            </div>
+            {{if .Consequence}}<p class="datapath-note">{{.Consequence}}</p>{{end}}
+        </div>
+        {{end}}
+    </div>
+</div>
+{{end}}
+
 {{if and .Stack.Deployed .MigrateTargets}}
 <div class="app-info-card" style="margin-top:1rem">
     <h3>Áthelyezés másik tárhelyre</h3>