[playground] bug fixes & UX improvements (#34499) #1499

Job	Run time
Cache Runtime, Compiler node_modules	1s
Discover flow inline configs	1d 0h 0m 0s
Cache Runtime node_modules	1s
yarn test ${{ matrix.params }} (Shard ${{ matrix.shard }})	-1s
yarn build and lint	-1s
Test eslint-plugin-react-hooks	-1s
Run sizebot	-1s
Flow check ${{ matrix.flow_inline_config_shortname }}	0s
Process artifacts combined	0s
Build DevTools and process artifacts	0s
Check flags	0s
Run fixtures Flight tests	-1s
yarn test-build	-1s
Run DevTools e2e tests	0s
Check release dependencies	0s
Search build artifacts for unminified errors	0s
Check fixtures DOM (stable)	-1s
Confirm generated inline Fizz runtime is up to date	0s
Merge DevTools artifacts	0s
	23h 59m 55s

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