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>

libs/workspace/shell/feature/src/lib/workspace-sources/workspace-sources.component.scss

@@ -123,10 +123,3 @@
 .sort-failing-first__check--off {
     visibility: hidden;
 }
-
-// UI-kit menu panel. The panel renders in the overlay container, so the
-// rule is global; it ships with the components that use `class="app-menu"`
-// rather than in the app's initial stylesheet.
-::ng-deep .mat-mdc-menu-panel.app-menu {
-    @include controls.menu-panel;
-}