Docs: SEO, lychee hardening, custom 404, and gallery improvements #4294

Job	Run time
Lint Gate	1m 15s
Detect File Changes	12s
Github (ubuntu, mpi, debug, true)	1h 46m 5s
Github (ubuntu, mpi, no-debug, true)	1h 33m 0s
Github (macos, mpi, debug, false)	59m 45s
Github (ubuntu, mpi, debug, false)	3h 35m 1s
Github (ubuntu, no-mpi, single, no-debug, false)	30m 10s
Github (macos, mpi, no-debug, false)	1h 17m 42s
Georgia Tech \| Phoenix (gpu-acc)	1h 5m 59s
Georgia Tech \| Phoenix (cpu)	1h 8m 15s
Oak Ridge \| Frontier (gpu-acc)	1s
Github (ubuntu, mpi, no-debug, false)	2h 16m 22s
Georgia Tech \| Phoenix (gpu-omp)	10m 2s
Oak Ridge \| Frontier (AMD) (gpu-omp)	1s
Oak Ridge \| Frontier (cpu)	2h 39m 26s
Oak Ridge \| Frontier (AMD) (cpu)	1s
Oak Ridge \| Frontier (gpu-omp)	1s
	17h 3m 18s

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