style(ui): ADR and one global kit layer for menus, select panels and destructive buttons (#1936)

* docs(ui): record the Angular Material role decision in the UI guidelines

Angular Material stays the behaviour and accessibility layer; the look comes
from the design kit through mat.*-overrides() on --app-* tokens in the shared
partials, kit-only components build on CDK, and plain actions may become
native buttons. Records the measured Material and CDK share of the initial
bytes, why a replacement would not pay, and the v22 behaviour changes to
keep covered in E2E.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* style(ui): one global kit layer for menus, select panels and destructive buttons

- `<mat-menu class="app-menu">` gets the kit panel from one rule in
  styles.scss; the two lazy components drop their `::ng-deep` copies.
- Select option panels follow the same panel: bordered, 10px radius, 6px
  padding, 36px rows at 13px, the chosen row on the list-selection tokens.
- `.app-destructive-button` is the kit's red tint on the `--app-danger-*`
  tokens (tinted fill, red text, no ripple, 40% opacity when disabled)
  instead of a solid error fill, for filled, text, outlined and icon
  buttons.
- The backdrop blur is scoped to the dark backdrop the CDK gives modal
  overlays; menus, selects and popovers open over a transparent backdrop
  that no longer matches the rule.
- `mat.elevation-classes()` is dropped: nothing uses `.mat-elevation-z*`,
  and its 25 rules cost 4.4 KB of the initial stylesheet. The stack now
  measures 1,595,843 initial bytes (was 1,597,764).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* test(e2e): wait for focus to enter an opened menu before navigating it

Material focuses a menu's first item after the next render, which the
zoneless scheduler runs on a later task than the keydown that opened it.
The panel is visible before that, so End sent as soon as it appeared still
reached the trigger: on the Linux runner the Sources row-menu delete test
then found "Remove playlist" inactive on every retry. `waitForMenuFocus`
polls for the active element inside the open menu; the Sources keyboard
and switcher keyboard tests use it before their first navigation key.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

apps/electron-backend-e2e/src/sources-keyboard.e2e.ts

@@ -9,6 +9,7 @@ import {
     waitForM3uCatalog,
     writeTemporaryM3uFile,
 } from './electron-test-fixtures';
+import { waitForMenuFocus } from './menu-keyboard';
 
 // ---------------------------------------------------------------------------
 // A source row opens from the keyboard. Each row has its own Tab stop: the
@@ -217,6 +218,7 @@ test.describe('Electron Sources keyboard', () => {
                 name: 'Remove playlist',
             });
             await expect(remove).toBeVisible();
+            await waitForMenuFocus(page);
             await page.keyboard.press('End');
             await expect(remove).toBeFocused();
             await page.keyboard.press('Enter');