fix(tui)!: query the terminal background once

[orhun]

Description of change

fixes #59

Also adds a new CLI argument for overriding the accent color.

How has this been tested? (if applicable)

Locally.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 3.35%. Comparing base (aba6112) to head (b3c7744).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tui/state.rs	0.00%	2 Missing ⚠️
src/lib.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #62      +/-   ##
========================================
+ Coverage   3.34%   3.35%   +0.01%     
========================================
  Files         19      19              
  Lines       2399    2393       -6     
========================================
  Hits          80      80              
+ Misses      2319    2313       -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.