fix(picker.list): correct row2idx calculation in reverse mode

[Tokamak-USTC]

Description

This PR addresses an issue where cursor movement and flash.nvim integration behave abnormally when using picker.list with a reverse layout (e.g., telescope).

The issue was caused by a mismatch between the item index (idx) and the visual row (row) in reverse mode.

• In function row2idx(list.lua:203): ret = row + self.top - 1 the original return value was: self.state.height - ret + 1 which expands to: self.state.height - (row + self.top - 1) + 1 = self.state.height - row - self.top + 2
• For row in the range 1..self.state.height, ret ranges from self.top to (self.top + self.state.height - 1), so the return value’s minimum is roughly -self.top + 2，which can be less than zero.

This fix ensures that:

• Cursor navigation correctly maps to the intended visual item in reverse lists.
• flash jumps target the correct item regardless of the list direction.

Related Issue(s)

Fixes #2605

Screenshots

after:

20251210-000603.mp4