[tlouisse]

Announce live regions that render inside a shadow root

Fixes #251.

A live region whose content is rendered inside its own shadow
root (host element with aria-live, message rendered into the shadow root) is
never announced, while the same region in the light DOM is.

Three coupled causes, each verified against 0.33.0:

1. observeDOM observes the container with subtree: true, and a
   MutationObserver does not cross shadow boundaries, so shadow root changes
   are never seen.
2. Rendering into a shadow root targets the ShadowRoot itself;
   getElementFromNode resolves a ShadowRoot to undefined because it only
   falls back to parentElement.
3. getLiveRegionAttributes walks up with parentElement only, so the
   aria-live attribute on the host is unreachable from inside its shadow root.

What this changes

• observeDOM: observes node plus every shadow root inside it, and wraps
  attachShadow so shadow roots attached later are observed as they are created.
  Without the wrap, the first content of a newly attached shadow root is missed:
  observation starts after that content exists and MutationObserver does not
  replay it. Both are undone on teardown.
• getElementFromNode: a ShadowRoot target maps to its host.
• getLiveSpokenPhrase: the ancestor walk crosses the shadow boundary
  (assignedSlot ?? parentElement ?? getRootNode().host ?? null).

Tests

New: test/int/ariaLiveShadowRoot.int.test.ts, covering both mutation shapes:

• a host with aria-live whose children are replaced through its shadow root
  (mutation target is the ShadowRoot);
• a live region that lives inside a shadow root and gets a text update
  (the walk has to cross the boundary).

Evidence on this branch:

jest test/int/ariaLiveShadowRoot.int.test.ts test/int/ariaLive.int.test.ts
  Test Suites: 2 passed, 2 total   Tests: 9 passed, 9 total

jest test/int
  Test Suites: 57 passed, 57 total   Tests: 330 passed, 330 total

tsc --noEmit -p tsconfig.json  -> 0 errors
eslint src test/int/...        -> clean

Both new tests fail on main without the source change (2 failed, the log stops
after "button, Trigger shadow live region"), so they are regression tests
rather than tests that pass either way.

Context

Found while adding screen reader tests for @lion/ui (ing-bank/lion), where
<lion-input-iban> renders its invalid message in the shadow root of
lion-validation-feedback with aria-live="assertive". NVDA and VoiceOver
announce that message; the virtual reader did not, so the test could not pin it
down locally. With this fix the virtual run speaks
"assertive: Error,, Please enter a valid IBAN.".

(Separate, cosmetic: the doubled comma comes from joining the additions phrase
and the text phrase of the same live region. Happy to look at that separately if
you want it tidied - it is not needed for this fix.)