test(web-e2e): reach row buttons with Option+Tab on WebKit (#1629)

The two "channel scrolling keeps focus after selection" cases (and the
Xtream "channel focus and separate scrollbar" cases, which press Tab the
same way) failed deterministically on Playwright WebKit while passing on
Chromium and Firefox. Playwright's WebKit emulates Safari's default
keyboard preference, under which plain Tab visits only text fields and
links: from the focused channel pane the key landed on the sidebar search
field instead of the first row button. Option+Tab reaches the button and
then the favorite action in the same DOM order Chromium's Tab follows, so
the app's focus contract (ChannelScrollFocusDirective) is intact and this
is Safari's Tab semantics, not an app bug.

Add a `pressTab` E2E helper that presses Alt+Tab only on webkit and keeps
the literal Tab / Shift+Tab on chromium and firefox, use it at the four
Tab presses toward buttons, and note Safari's behaviour in the keyboard
scrolling contract.

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

docs/architecture/iptvnator-ui-guidelines.md

@@ -162,7 +162,10 @@ ArrowUp/Down, PageUp/Down, Home/End and Space retain native scrolling there;
 scroll keys do not bubble into document-level player shortcuts. A row's main
 button remains separate from favorite/info actions, supports native Enter and
 Space activation, and retains keyboard focus on activation. Tab/Shift+Tab use
-the normal DOM order. Scrolling from a virtual row moves focus to its viewport
+the normal DOM order; Safari's default keyboard preference skips buttons on
+plain Tab, so there the row button is reached with Option+Tab (WebKit E2E
+runs press it through `pressTab` in `apps/web-e2e/src/e2e-helpers.ts`).
+Scrolling from a virtual row moves focus to its viewport
 before CDK can recycle the row; asynchronous data updates never move focus.
 Xtream aligns a newly selected channel only when it is outside the viewport;
 updates to the same selected ID never re-align it. A smooth scroll to an