chore(deps): upgrade react to 19.2.7 and react types to 19.x (#1154)

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.

package.json

@@ -20,8 +20,8 @@
     "@react-spring/web": "10.0.3",
     "@ruffle-rs/ruffle": "0.2.0",
     "@types/node": "20.19.37",
-    "@types/react": "18.2.25",
-    "@types/react-dom": "18.2.10",
+    "@types/react": "19.2.16",
+    "@types/react-dom": "19.2.3",
     "@use-gesture/react": "10.3.1",
     "@vercel/analytics": "^1.6.1",
     "ace-builds": "1.41.0",
@@ -37,9 +37,9 @@
     "json-stringify-pretty-compact": "4.0.0",
     "lodash": "4.18.0",
     "memoizee": "0.4.15",
-    "react": "19.1.2",
+    "react": "19.2.7",
     "react-ace": "14.0.1",
-    "react-dom": "19.1.2",
+    "react-dom": "19.2.7",
     "react-i18next": "16.6.6",
     "react-router-dom": "6.30.2",
     "react-router-hash-link": "2.4.3",