fix(textinput): account for scroll offset in hardware Cursor() X position

[syf2211]

Summary

Fix textinput.Model.Cursor() to use the scroll-adjusted visible column (m.pos - m.offset) instead of the absolute cursor position (m.Position()), matching how View() already renders the cursor.

Fixes #1001

Motivation

When input text is wider than the configured width, the textinput scrolls horizontally. View() correctly uses m.pos - m.offset for the visible cursor column, but Cursor() used the absolute position. This caused the hardware cursor (used with SetVirtualCursor(false)) to appear at the wrong column when the input was scrolled.

Changes

• textinput/textinput.go: In Cursor(), replace m.Position() with max(0, m.pos-m.offset) when computing xOffset.
• textinput/textinput_test.go: Add TestCursorXAccountsForScrollOffset — sets a 30-character value in a width-20 input with the cursor at position 15 (offset=10, visible column=5) and asserts Cursor().X == 7 (visible column + prompt width).

Tests

go test ./textinput/... -v -run TestCursorXAccountsForScrollOffset  # PASS
go test ./...                                                      # PASS (all packages)

Notes

• The existing min(xOffset, m.width+promptWidth) clamp is unchanged.
• When text does not overflow (offset == 0), behavior is identical to before.
• Reviewed with composer-2.5 sub-agent: APPROVED.