feat(ui): 49 themes with matched syntax highlighting + preview mode #1042

Job	Run time
test	37s
build	1m 23s
smoke-binaries (windows-latest, plannotator-win32-x64.exe)	1m 1s
install-script-smoke (ubuntu-latest, plannotator-linux-x64)	19s
smoke-binaries (ubuntu-latest, plannotator-linux-x64)	18s
npm-publish	1m 2s
attest	0s
release	0s
	4m 40s

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