Request: Add hover text on single-letter buttons

[parker-research]

For example, the C button to Copy a custom TLE is entirely unclear what it does.

[aweeri]

Hi and thanks! Added to the TODO.

[TianHengZhuang]

Hi! I'd like to take a stab at this one. I had a look at the TLE manager code in src/ui.c — the single-letter buttons on each custom TLE row (e.g. the "C" copy button and "X" delete button) are plain GuiButton calls with no hint about what they do.

My plan: add tooltips for those buttons using RayGui's GuiSetTooltip() right before the button draws, so hovering shows something like "Copy TLE to clipboard" / "Remove TLE". It's a small, localized change in ui.c, no new dependencies, and consistent with the existing UI style.

Happy to open a PR if that sounds good — or let me know if you'd prefer a different approach.