chore(html): simplify Gantt templates #5120

Job	Run time
CI \| Unit	1s
Status check > Unit	1s
CI \| Visual	1s
Lint scripts / run	45s
Render test pages / verify	9s
Compile themes / run	47s
Lint styles / run (default)	1m 25s
Lint styles / run (bootstrap)	1m 27s
Lint styles / run (material)	1m 23s
Lint styles / run (classic)	1m 34s
Lint styles / run (fluent)	1m 6s
Render test pages / run	3m 11s
Status check > Lint scripts	1s
Status check > Lint styles	1s
Status check > A11y / prepare	1s
Create screenshots / run (default)	2m 21s
Create screenshots / run (bootstrap)	2m 31s
Create screenshots / run (material)	2m 32s
Create screenshots / run (classic)	2m 23s
Create screenshots / run (fluent)	2m 31s
Status check > A11y / run-checks (1)	2m 43s
Status check > A11y / run-checks (2)	3m 9s
Status check > A11y / run-checks (3)	2m 24s
Status check > A11y / run-checks (4)	2m 40s
Detect changes	21s
Status check > Visual	1s
	35m 29s

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