feat(shares): R-7b Parts 4-6 — shares restore, samba liveness, UI truth-up

Part 4 — restore: RestoreSharesScratch + PlaceSharesRestore as SIBLINGS of the
per-app scratch/place pair. Files merged missing-only (never overwriting), each
destination PREFIX-ASSERTED against registered LIVE storage roots; definitions
merged with existing-wins; ReconcileSamba via a seam (backup must not import
stacks); credential restored best-effort into the samba named volume.
New routes POST /backup/shares/{restore,place} + a restore-page entry that renders
'Megosztasok', never the raw reserved key.
Also adds scratchJoin: reconstructing an absolute captured path under a scratch
must strip the volume name rather than rely on filepath.Join.

Part 5 — liveness: EffectiveProtected gains a settings-backed dynamic extra so the
samba CONTAINER (not the stack name — they differ) is watched exactly while sharing
is on. FINDING: the issue -> health 'fail' -> existing health_critical event ->
alert -> Hungarian degradation e-mail path needs NO further change, and introduces
no new event type, so the allowlist gotcha does not apply.

Part 6 — UI: per-tier backup status lines on the Megosztas page (amber only on
deviation). Verified the two warning-prose sites (offbox_capture/tier2_capture)
only ever receive per-app stack names, so no mapping is needed there.

RED-PROOFS RUN AND REVERTED (both fired):
  4. prefix-assert removed        -> place-guard traversal test FAILS
  5. dynamic samba extra removed  -> Scenario E enabled-case FAILS

controller/internal/web/templates/backups_restore.html

@@ -102,6 +102,25 @@
     {{else}}
     <p class="form-hint">Nincs távoli mentésre jelölt alkalmazás — a kijelölés a <a href="/backups/remote">Távoli mentés</a> oldalon történik.</p>
     {{end}}
+
+    <!-- R-7b: the shares source. Not an app row — it has no per-app toggle and no recovery unit —
+         so it is its own entry. The reserved `_shares` key never appears here; the label always
+         comes from the display mapping. -->
+    {{if .SharesRestoreOffered}}
+    <div class="app-row-list" style="margin-top:1rem">
+        {{template "app_list_row" dict "Slug" "" "Name" .SharesDisplayName}}
+            <form method="POST" action="/backup/shares/restore" style="display:inline">{{$.CSRFField}}
+                <button type="submit" class="btn btn-xs btn-outline">Megosztások visszaállítása</button>
+            </form>
+            {{if .SharesScratchReady}}
+            <form method="POST" action="/backup/shares/place" style="display:inline">{{$.CSRFField}}
+                <button type="submit" class="btn btn-xs btn-outline">Helyreállítás az élő adatok közé (csak a hiányzó fájlok)</button>
+            </form>
+            <span class="form-hint" style="display:block;margin-top:.25rem">A meglévő fájlokat nem írja felül. A már létező megosztás-beállítások változatlanok maradnak.</span>
+            {{end}}
+        {{template "app_list_row_end"}}
+    </div>
+    {{end}}
 </div>
 {{end}}