Refactor code for consistency and enhanced functionality.

- Normalize path handling for buffer operations, supporting tilde expansion and absolute paths.
- Introduce `DisplayNameFor` to uniquely resolve buffer display names, minimizing filename clashes.
- Add new commands: `ShowWorkingDirectory` and `ChangeWorkingDirectory`.
- Refine keybindings and enhance existing commands for improved command flow.
- Adjust GUI and terminal renderers to display total line counts alongside filenames.
- Update coding style to align with project guidelines.

Command.h

@@ -74,6 +74,8 @@ enum class CommandId {
 	MarkAllAndJumpEnd, // set mark at beginning, jump to end (C-k a)
 	// Direct navigation by line number
 	JumpToLine, // prompt for line and jump (C-k g)
+	ShowWorkingDirectory, // Display the current working directory in the editor message.
+	ChangeWorkingDirectory, // Change the editor's current directory.
 	// Meta
 	UnknownKCommand, // arg: single character that was not recognized after C-k
 };