Linux portable release searches assets in /usr/share/ludo instead of current directory

[railroad-code]

Environment:

• Fedora Silverblue 44
• Ludo v0.22.5 (Linux Wayland x86_64 release)
• Running directly from extracted release archive

Steps to reproduce:

1. Download and extract Ludo-Linux-wayland-x86_64-0.22.5

2. Open a terminal in the extracted directory

3. Run:

   ./ludo

Expected behavior:
Ludo should load its assets and database from the extracted release directory.

Actual behavior:
Ludo tries to load files from /usr/share/ludo and crashes.

Output:

2026/06/01 15:00:50 Can't load game database: open /usr/share/ludo/database: no such file or directory
panic: open /usr/share/ludo/assets/font.ttf: no such file or directory

goroutine 1 [running, locked to thread]:
github.com/libretro/ludo/video.(*Video).Configure(0xc000248000, 0x0?)
/home/runner/work/ludo/ludo/video/video.go:135 +0xa45
github.com/libretro/ludo/video.Init(...)
/home/runner/work/ludo/ludo/video/video.go:52
main.main()
/home/runner/work/ludo/ludo/main.go:120 +0x50b

Notes:
It appears the release binary is using a hardcoded asset path (/usr/share/ludo) instead of resolving assets relative to the executable location.

Originally posted by @railroad-code in #586