Deps: Revisit deferred major upgrades (eslint 10, react-day-picker 10, react-hooks 7, @eslint/js 10)

[prem22k]

Four major upgrades were tested this session and deferred because they require code migration, not just a version bump. Each currently blocks CI or needs an explicit change:

1. eslint 9 to 10 + @eslint/js 10 + eslint-plugin-react-hooks 7 - react-hooks v7 recommended adds 95 new errors (55 setState-in-effect, 22 no-unused-vars, 9 impure-render, 5 no-useless-assignment). Needs either code fixes across ~30 components or deliberate rule-config decisions.
2. react-day-picker 9 to 10 - shadcn calendar.tsx classNames API + component model changed; needs a calendar rewrite.

Work needed per package: apply upgrade, fix migration, keep lint/typecheck/build green, run tests. Do them one at a time in separate PRs.

See closed dependabot PRs 200/201/203/208/221 for the version targets.