Add scoped postbox template previews

src/govoplan_postbox/backend/manifest.py

@@ -473,7 +473,12 @@ manifest = ModuleManifest(
                 "Hierarchy copies are independent deliveries with their own evidence; "
                 "vacancy escalation is delayed and separately auditable. Message expiry "
                 "or withdrawal blocks future content access but cannot retract plaintext "
-                "already copied, exported, or printed."
+                "already copied, exported, or printed. Subtree templates select one "
+                "explicit organization structure and optional relation types. Their "
+                "read-only impact preview reports generated addresses, current holders, "
+                "vacancy, collisions, cycles, depth limits, and ambiguous paths without "
+                "creating templates or Postboxes. Grouping totals include only source "
+                "Postboxes currently visible to the account."
             ),
             layer="configured",
             documentation_types=("admin", "user"),
@@ -506,6 +511,7 @@ manifest = ModuleManifest(
                     "postbox.field.classification",
                     "postbox.field.retention",
                     "postbox.field.hierarchy-routing",
+                    "postbox.action.preview-template",
                     "postbox.field.recipients",
                     "postbox.action.archive",
                     "postbox.action.retire-template",
@@ -513,6 +519,7 @@ manifest = ModuleManifest(
                 ],
                 "consequence_classes": {
                     "publish_template": "Freezes an immutable address and routing revision for future materialization.",
+                    "preview_template": "Reads current organization, hierarchy, and incumbency state without materializing any address or Postbox.",
                     "retire_template": "Stops new revisions and materialization while retaining existing addresses.",
                     "archive_postbox": "Stops new delivery while retaining messages, receipts, and evidence.",
                     "delete_grouping": "Deletes only the personal projection; source Postboxes and messages remain unchanged.",