feat: add web UI

[dundee]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 47.43590% with 205 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.68%. Comparing base (99a7f2a) to head (1f6811d).

Files with missing lines	Patch %	Lines
webui/webui.go	44.54%	56 Missing and 5 partials ⚠️
webui/handlers.go	44.70%	45 Missing and 2 partials ⚠️
webui/server.go	17.39%	38 Missing ⚠️
webui/hub.go	26.08%	16 Missing and 1 partial ⚠️
webui/tree.go	82.50%	7 Missing and 7 partials ⚠️
cmd/gdu/app/app.go	0.00%	11 Missing ⚠️
webui/embed.go	25.00%	7 Missing and 2 partials ⚠️
webui/browser.go	61.11%	6 Missing and 1 partial ⚠️
cmd/gdu/main.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #617      +/-   ##
==========================================
- Coverage   86.89%   84.68%   -2.22%     
==========================================
  Files          55       62       +7     
  Lines        6526     6915     +389     
==========================================
+ Hits         5671     5856     +185     
- Misses        658      844     +186     
- Partials      197      215      +18     

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