feat(tui): support configurable cursor style, blink, and color

[fanyu]

What does this PR do?

Fixes #11305 by adding configurable cursor behavior for TUI textareas.

Changes:

• add cursor_style (block | line | underline) to TUI config
• add cursor_blink (boolean) to TUI config
• add cursor_color (hex #RRGGBB or theme color key) to TUI config
• apply these options to TUI textareas (prompt/question/permission/dialog/export)
• update docs for TUI config options

How did you verify your code works?

• verified schema/typecheck for new TUI config options (config.ts + tui-schema.ts)
• verified all touched textarea call sites now pass cursor style and color from TUI config
• CI: typecheck and unit checks passed in previous runs on this branch; e2e failures were addressed by follow-up terminal toggle fix in app

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