Add swap file journaling for crash recovery.

- Introduced `SwapManager` for buffering and writing incremental edits to sidecar `.kte.swp` files.
- Implemented basic operations: insertion, deletion, split, join, and checkpointing.
- Added recovery design doc (`docs/plans/swap-files.md`).
- Updated editor initialization to integrate `SwapManager` instance for crash recovery across buffers.

TerminalFrontend.cc

@@ -55,6 +55,8 @@ TerminalFrontend::Init(Editor &ed)
 	prev_r_ = r;
 	prev_c_ = c;
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
+	// Attach editor to input handler for editor-owned features (e.g., universal argument)
+	input_.Attach(&ed);
 	return true;
 }
 
@@ -100,4 +102,4 @@ TerminalFrontend::Shutdown()
 		have_orig_tio_ = false;
 	}
 	endwin();
-}
+}