fix(textarea): avoid phantom soft-wrap and unstick vertical cursor

[Solaris-star]

Summary

Fixes #887.

When a soft-wrapped line exactly filled the textarea width, wrap() used >= width and created a phantom blank line. Vertical navigation also stopped one display column early because setCursorLineRelative broke when offset >= CharWidth-1.

Changes

• Use > width in the final wrap() width check so content that exactly fits does not spawn an extra line
• Compare offset >= CharWidth when restoring the horizontal cursor column after vertical moves
• Update TestView cursor expectations for exact-width lines
• Add regression tests for phantom wrap lines and cursor-down from a full-width line

Test plan

• go test ./textarea/