fix(ui): restore window settings when using position=current

[aweis89]

Summary

When using position = 'current' configuration, opencode modifies window options (wrap, number, relativenumber, signcolumn, etc.) on the current window. This PR ensures those settings are saved before modification and restored when opencode is closed.

Problem

Previously, when closing opencode with position = 'current', the window would retain opencode's settings (e.g., wrap=true, number=false) instead of reverting to the user's original settings.

Solution

• Save original window option values before modifying them (only when position = 'current')
• Restore saved values when closing opencode
• Store saved options in state.saved_window_options

Files Changed

• lua/opencode/state.lua - Added saved_window_options field to state
• lua/opencode/ui/output_window.lua - Helper function set_win_option() that saves original values before setting
• lua/opencode/ui/ui.lua - Restore saved options in close_windows()