Add biome lint fixes

[cmdcolin]

This addresses some things flagged from the biome linter (https://biomejs.dev/linter/). it doesn't yet add biome to the CI, but that could be a next step. there are many valid things it triggers on. in particular it was good at catching:

• usage of implicit any types in typescript, especially when it is supposed to be 'inferred from usage' but wasn't really
• better exhaustive deps rule for react hooks (compared to eslint exhaustive deps rule)
• caught some missing eqeqeq (triple ===)
• caught some usage of index in react key, which is needed in some of our cases, but can be done better (adding something in addition to the idx is often good)
• changed more things to use template strings instead of string addition