Bump react and react-dom 19.1.2 -> 19.2.7 and @types/react and
@types/react-dom from v18 to v19. Keeps babel-plugin-react-compiler,
which is a separate build-time tool, not part of the React 19 runtime.
The @types v19 upgrade surfaced 21 type-only errors, all fixed without
runtime behavior changes:
- useRef<T>() now requires an explicit argument: pass undefined
- DOM element refs are RefObject<T | null>: widen PostFormFields and
AdvancedSettings ref prop types accordingly
- retype reply-modal onInput handler to FormEvent + currentTarget
- add a null guard for the boards-bar search input
- update test mocks for stricter cloneElement/forwardRef typings
Verified: type-check, lint, 1051 tests, and build pass; react-doctor
score unchanged at 54; browser smoke across Chromium/Firefox/WebKit
plus mobile viewport clean.