[DevTools] Move Timeline to footer instead of header (facebook#34617)

One thing that always bothered me is that the collapse buttons on either
side of the toolbar looks like left/right buttons which would conflict
with some steps buttons I plan to add. Another issue is that we'll need
to add more tool buttons to the top and probably eventually a Search
field. Ideally this whole section should line up vertically with the
height of the title row.

I also realized that all UIs that have some kind of timeline control
(and play/pause/skip) do that in the bottom below the content. E.g.
music players and video players all do that. We're better off playing
into that structure since that's the UI analogy we're going for here.
Makes it clearer what the weird timeline is for.

By moving it to the bottom it also frees up the top for the collapse
buttons and more controls.

__Horizontal__

<img width="794" height="809" alt="Screenshot 2025-09-26 at 3 40 35 PM"
src="https://github.com/user-attachments/assets/dacad9c4-d52f-4b66-9585-5cc74f230e6f"
/>

__Vertical__

<img width="570" height="812" alt="Screenshot 2025-09-26 at 3 40 53 PM"
src="https://github.com/user-attachments/assets/db225413-849e-46f1-b764-8fbd08b395c4"
/>

DiffTrain build for [2622487](facebook@2622487)

Author: pull[bot]

compiled-rn/VERSION_NATIVE_FB

@@ -1 +1 @@
-19.2.0-native-fb-047715c4-20250925
+19.2.0-native-fb-2622487a-20250926

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<996b6a5d86031131e6eb91adeaaed7ab>>
+ * @generated SignedSource<<98a5b3872f3c838b70744d464a21be12>>
  */
 
 "use strict";
@@ -404,5 +404,5 @@ __DEV__ &&
     exports.useFormStatus = function () {
       return resolveDispatcher().useHostTransitionStatus();
     };
-    exports.version = "19.2.0-native-fb-047715c4-20250925";
+    exports.version = "19.2.0-native-fb-2622487a-20250926";
   })();

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-prod.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<7fe4d54761a021892778289a65d877db>>
+ * @generated SignedSource<<0431d9ee2e609bb2983edaa436399c16>>
  */
 
 "use strict";
@@ -203,4 +203,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.2.0-native-fb-047715c4-20250925";
+exports.version = "19.2.0-native-fb-2622487a-20250926";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-profiling.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<7fe4d54761a021892778289a65d877db>>
+ * @generated SignedSource<<0431d9ee2e609bb2983edaa436399c16>>
  */
 
 "use strict";
@@ -203,4 +203,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.2.0-native-fb-047715c4-20250925";
+exports.version = "19.2.0-native-fb-2622487a-20250926";