feat: add configurable vertical position setting

[MdTanjeemHaider]

What

The launcher window was always placed at a hardcoded physical y=100 regardless
of screen resolution. Monitors with different resolution put the window in odd locations at times.

This PR replaces the hardcoded value with a user-configurable "Vertical Position" setting (default: 30% from top, range: 5–85%).

Changes

• src-tauri/src/main.rs

  • Added WINDOW_Y_PERCENT static (default 30).
  • Added compute_window_y_phys(). This calculates physical pixel offset from monitor height × percentage.
  • Added get_window_y_percent Tauri command.
  • Added set_window_y_percent Tauri command. The setter saves to settings.json and immediately repositions the window for live preview.
  • show_main_window and reset_window both use compute_window_y_phys against the monitor the cursor is currently on.

• src/index.html

  • New settings row with a range slider.

• src/main.js

  • Loads saved value at startup, live-updates on drag, resets to 30% when "Reset Settings" is clicked.

Tested on

• 1920x1080
• 1920x1200 (Set to vertical mode)