enhancement: add text selection to the virtual keyboard (select all, select stem) #44

Summary

Support a selected range in the keyboard model so rename can pre-select the name without the extension, and typing replaces the selection.

Motivation

Needed for the rename flow (example-file|.zip with example-file selected).

Requirements

• Selection range in VirtualKeyboard; typing or Backspace replaces/deletes the selection.
• API to pre-select a range when opening (used by feat: rename files and folders with extension-preserving selection #11).
• Select all action from the … menu.

Controller UX

Selected text is highlighted; typing replaces it; cursor keys collapse the selection.

Technical Notes

Model change in ControlFS.Core/Text/VirtualKeyboard.cs plus rendering.

Acceptance Criteria

• Opening rename on example-file.zip selects example-file; typing novo yields novo.zip.

Testing

Unit tests for new branches and for every bug reproduced before a fix (no trivial variations, see AGENTS.md).

Dependencies

• Depends on enhancement: improve text cursor navigation (visible caret, jump to start/end) #43 — enhancement: improve text cursor navigation (visible caret, jump to start/end)

Priority: high · Milestone: 3 · Virtual Keyboard UX