perf(grid): improve layout responsiveness and remove selection transitions (#2400)

This PR addresses performance issues in the media grid by disabling
resource-intensive CSS transitions and ensuring immediate layout
updates. Previously, the default `0.2s` transition duration for grid
reshuffling was causing browser overloads on devices with multiple live
video viewers, leading to stuttering and occasionally missing
short-lived video events.

## Changes

### 1. Disable Masonry Transitions
- Set `transitionDuration` to `0` in the Masonry configuration to
eliminate CSS-driven animations during layout.
- Set `stagger` to `0` to ensure all items move simultaneously and
instantly.
- Set `resize` to `false` in the Masonry config, as window resizing is
already efficiently handled by the controller's `ResizeObserver`.

### 2. Immediate Layout Updates
- Introduced a `_forceLayout()` method in `MediaGridController` that:
- Cancels any pending throttled layout calls to avoid redundant work.
- Triggers a browser reflow via `getBoundingClientRect()` to ensure all
element dimensions are synchronized before the next draw.
    - Forces an immediate Masonry layout.
- Integrated `_forceLayout()` into `selectCell()` and `unselectAll()` to
guarantee the grid updates at the exact moment a user interacts with it.

### 3. Test Alignment
- Updated `tests/components-lib/media-grid-controller.test.ts` to
reflect the changes.

## Performance Impact
By eliminating timed transitions, we significantly reduce the peak CPU
and GPU load during grid selection changes. This results in a much
snappier UI where video viewers snap into position instantly, preventing
the "shuttering" effect and ensuring that time-critical video playback
is not interrupted by heavy animation cycles.

---------

Co-authored-by: dermotduffy <dermot.duffy@gmail.com>

tests/components-lib/media-grid-controller.test.ts

@@ -17,7 +17,11 @@ import {
 
 vi.mock('lodash-es', async () => ({
   ...(await vi.importActual('lodash-es')),
-  throttle: vi.fn((fn) => fn),
+  throttle: vi.fn((fn) => {
+    const throttled = vi.fn(fn) as unknown as { cancel: () => void };
+    throttled.cancel = vi.fn();
+    return throttled;
+  }),
 }));
 
 const masonry = mock<ExtendedMasonry>();
@@ -394,7 +398,7 @@ describe('MediaGridController', () => {
       expect.objectContaining({
         initLayout: false,
         percentPosition: true,
-        transitionDuration: '0.2s',
+        transitionDuration: 0,
       }),
     );
   });