Address major concerns from v0.1.0 release

[claytercek]

After the v0.1.0 release (#11), there was some feedback from the community that helped call attention to some bugs!

• Fixes the search contrast issue. Highlighted terms are now far more visible, following the VSCode yellow highlight pattern
• Improves file tree readability, again following VSCode precedent
  • higher contrast on ignored/hidden files
  • default foreground color for unchanged files
• Changes variable color to default foreground color
• improves terminal readability, using theme default foreground color instead of dimmed

I avoided addressing the more subjective complaints in this PR, instead focusing on functional and accessibility issues. I suggest we open additional issues/discussions to come up with resolutions resolutions for those, as they mostly seem like a matter of personal preference.

Thanks! 😄

[PyaeSoneAungRgn]

Thanks you so much