fix(hyprland): generate inactive border gradients in Lua

[igmg6-ua]

Problem

Hyprland 0.55 represents gradients in Lua as a table. The generator already
uses this representation for active_border, but serializes multi-color
inactive_border values as a quoted string, causing an invalid color error.

Fix

Apply the existing active-border gradient serialization logic to
inactive_border, while preserving the current single-color output.

Keep the duplicated code, so calls to this function doesnt broke, can be fixed with a follow-up refactor.

Testing

• Tested with Hyprland 0.55.4 and Ambxst's Frutiger Aero preset
• Verified two-color inactive gradients load without configuration errors
• Verified single-color inactive borders retain their existing representation