fix: replace JSX.Element with React types for React 19 compatibility (#732)

* fix: replace JSX.Element with React.ReactElement for React 19 compat

JSX.Element was removed from the global JSX namespace in React 19 types.
Components returning JSX.Element are no longer assignable to the updated
ReactNode return type, causing type errors for users on React 19.

Fixes #637

* Update src/storage.tsx

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update src/storage.tsx

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* docs: regenerate API reference after React 19 type fixes

* ci: trigger checks

* docs: regenerate API reference without skipErrorChecking flag

* ci: add React 18/19 type-check matrix job

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: tyler-reitz

.github/workflows/test.yaml

@@ -79,6 +79,27 @@ jobs:
           ./reactfire-${{ github.run_id }}/unpack.sh
       - name: Run tests
         run: npm run test
+  type-check:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        react: ["18", "19"]
+      fail-fast: false
+    name: Type check (React ${{ matrix.react }})
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+          cache: 'npm'
+      - name: Install deps
+        run: npm ci
+      - name: Install React ${{ matrix.react }} types
+        run: npm install --no-save react@${{ matrix.react }} react-dom@${{ matrix.react }} @types/react@${{ matrix.react }} @types/react-dom@${{ matrix.react }}
+      - name: Type check
+        run: npx tsc --noEmit
   publish:
     runs-on: ubuntu-latest
     name: Publish (NPM)