fix(tui): restore cursorUp line-start jump before history browsing

[4h9fbZ]

PR #1050 added editor boundary behavior where pressing Up on the first visual line of non-empty input jumps to the start of the line instead of doing nothing. Commit e4907b3b fixed draft restoration for prompt-history browsing, but changed cursorUp to always enter history whenever history exists. That made the start-of-line jump path unreachable for non-empty input with history.

This keeps both behaviors:

• If the editor is non-empty and the cursor is not at the start, Up jumps to the start of the current line.
• If the editor is empty, already browsing history, or the cursor is already at column 0 on the first visual line, Up enters/navigates history.
• Draft restoration from e4907b3b is preserved: after entering history from a draft, Down restores the draft state.

Tests were updated to cover the two-step non-empty flow: first Up jumps to the start of the draft, second Up enters history, and Down restores the draft.

[vegarsti]

@4h9fbZ Thanks a lot! I agree that e4907b3 regressed the behaviour you added earlier in #1050, and I've confirmed the behavior is back with this change.