Fix #13: Expose Pre-edit Backup restoration

Preserve full diff opcodes before grouping, route modal navigation to a two-axis viewport-sized scroller, and calculate side-by-side layout using terminal cell widths so tabbed Hosts File lines keep a stable divider.

README.md

@@ -20,6 +20,7 @@ on macOS and Linux.
 - Creates DNS Entries and manually refreshes their resolved IP addresses.
 - Gates every `/etc/hosts` mutation behind an explicit Privileged Mode.
 - Creates a timestamped Pre-edit Backup before Privileged Mode begins.
+- Restores the current session's Pre-edit Backup after explicit confirmation.
 - Supports undo and redo during the current Privileged Mode session.
 
 The application starts in Read-only Mode. Default Entries cannot be edited,
@@ -63,6 +64,7 @@ including persistence behavior and manual recovery.
 | --- | --- |
 | `Up` / `Down` | Select a Host Entry |
 | `Ctrl+E` | Enter or leave Privileged Mode |
+| `b` | Review and restore the session Pre-edit Backup |
 | `n` | Add a Host Entry |
 | `e` | Open the selected Host Entry in the Entry Editor |
 | `d` | Delete the selected Host Entry |
@@ -79,8 +81,8 @@ sorting, DNS refresh, movement, undo, and redo.
 ## Safety and known limitations
 
 - Reloading discards unsaved in-memory state.
-- Pre-edit Backups are not listed or restored by the TUI and have no retention
-  management. Manual recovery is documented in the user guide.
+- The TUI can restore only the Pre-edit Backup associated with the current
+  Privileged Mode session; it does not list old backups or manage retention.
 - Leaving Privileged Mode clears the application's session state but does not
   alter the user's cached sudo timestamp.
 - Serialization preserves Host Entries and comments semantically, but