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

Summary

Build on the existing caret support (VirtualKeyboard.MoveCaret, LB/RB, ◀▶ keys): a clearly visible caret, jump to start/end, and preserved text state.

Motivation

Editing the middle of a name (Control|FS) must be easy without closing the keyboard.

Requirements

• Visible, animated-free caret in the text field; caret position announced to Narrator.
• Jump to start/end (e.g. LT/RT while the keyboard is open).
• Cursor moves never alter the text or the current page/shift state.

Controller UX

LB/RB or ◀/▶ move one character (repeat when held via #42); LT/RT jump to start/end.

Technical Notes

VirtualKeyboard already tracks Caret; add start/end operations and rendering in ModalView.

Acceptance Criteria

• Typing in the middle of existing text inserts at the caret.
• Jumping to start/end works on long text.

Testing

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

Dependencies

• Depends on enhancement: hold-to-repeat for Backspace and cursor keys in the virtual keyboard #42 — enhancement: hold-to-repeat for Backspace and cursor keys in the virtual keyboard

Priority: high · Milestone: 3 · Virtual Keyboard UX