Fix the delete confirmation, which still promised permanence

Hardware testing caught the dialog saying 1 item will be permanently deleted. This cannot be undone while deletes now stage into the trash. Reworded to describe what actually happens, and deliberately without promising an undo button: that lives in a snackbar and is gone in seconds, whereas the trash keeps the item for a day. Also records that the trash has no screen of its own.

README.md

@@ -139,6 +139,11 @@ UI.** Translated UI text has to be supplied in `values-<locale>/`.
 
 ## Known limitations
 
+- **The trash has no screen of its own.** A delete now stages the item in a hidden
+  `.plainfiles-trash` folder on the same volume and keeps it for 24 hours, and the snackbar
+  offers Undo. Once that snackbar goes there is no in-app bin to browse or restore from — the
+  folder is reachable by turning on hidden files, but a proper trash screen is the obvious
+  follow-up.
 - **Sharing a file *out* only works in the all-files mode.** A SAF path is relative to the
   granted tree rather than a filesystem path, so it cannot be handed to `FileProvider`.
   Receiving a share and being picked from another app's chooser work either way: the first

app/src/main/res/values/strings.xml

@@ -114,10 +114,15 @@
     <string name="browser_kind_other">File</string>
 
     <!-- ===== Browser: delete + conflict ===== -->
-    <string name="browser_delete_title">Delete permanently?</string>
+    <!--
+      A delete stages into the trash rather than removing, so this must not promise
+      permanence. It also must not promise an undo button: that lives in the snackbar and
+      is gone within seconds, whereas the trash keeps the item for a day.
+    -->
+    <string name="browser_delete_title">Move to the trash?</string>
     <plurals name="browser_delete_body">
-        <item quantity="one">%1$d item will be permanently deleted. This cannot be undone.</item>
-        <item quantity="other">%1$d items will be permanently deleted. This cannot be undone.</item>
+        <item quantity="one">%1$d item will be moved to the trash, where it is kept for 24 hours before it is removed.</item>
+        <item quantity="other">%1$d items will be moved to the trash, where they are kept for 24 hours before they are removed.</item>
     </plurals>
     <string name="conflict_title">Items already exist here</string>
     <plurals name="conflict_body">