test(web): await the theme observer instead of a wall-clock budget

The AppRenderer "live theme flip" test had its inner `waitFor` raised twice
(bare assertion -> 1000ms -> 5000ms) and failed a third time at 5032ms under
`local:gate` load. The budget was never the problem.

Root cause: happy-dom 20.11.1's `MutationObserverListener` stores its dispatch
callback as `new WeakRef((record) => this.report(record))` — an arrow function
nothing else holds strongly. A GC between `observe()` and the mutation collects
it, `callback.deref()` returns undefined in `Node[reportMutation]`, and the
mutation is dropped silently and permanently. That is why the failure tracks
machine load rather than any wall-clock value, and why no raise ever fixed it.

Reproduced directly against 20.11.1: an observer on `documentElement`, three
forced `global.gc()` passes, then `setAttribute` — callback count 0. Without
the forced GC, 1. Upstream holds the arrow strongly in a private field from
20.11.2 onward; the same probe against the bumped copy reports 1.

So:

- bump `happy-dom`'s floor to `^20.11.2` (lockfile resolves 20.14.5), which is
  the actual fix;
- replace the 5000ms `waitFor` with `flipThemeAttributeAndAwaitObservers`, an
  awaited condition per AGENTS.md: a probe MutationObserver registered after
  the component's is notified after it, so resolving on the probe's callback
  proves the component's already ran. No polling, no timeout, nothing
  load-sensitive.
- use the same helper in the two negative theme tests, which is what makes
  their "not called" a real gate rather than a vacuous pass on a flip that was
  never delivered.

The file's 52 tests now run in ~120ms.

Closes #2384

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/package-lock.json

@@ -46,7 +46,7 @@
         "eslint-plugin-react-hooks": "^7.1.1",
         "eslint-plugin-react-refresh": "^0.5.2",
         "eslint-plugin-storybook": "^10.5.5",
-        "happy-dom": "^20.9.0",
+        "happy-dom": "^20.11.2",
         "playwright": "^1.58.2",
         "storybook": "^10.5.5",
         "tsup": "^8.5.1",
@@ -5264,9 +5264,9 @@
       "optional": true
     },
     "node_modules/happy-dom": {
-      "version": "20.11.1",
-      "resolved": "https://registry.npmjs.org/happy-dom/-/happy-dom-20.11.1.tgz",
-      "integrity": "sha512-XSt8tMzbW9ymE7687xztkO1ckR7qJNQ3LywY9vlYGhGi3zXrGBHuUo2Cl1ztZaICW+1eAGdkLbj6iwVqDT33kg==",
+      "version": "20.14.5",
+      "resolved": "https://registry.npmjs.org/happy-dom/-/happy-dom-20.14.5.tgz",
+      "integrity": "sha512-x/RzkpWO40bTjIoT30iQtt64FLLmH/iRcUCN2X//bLx7H3ifkdfPXyqsro/OYtqzIAhiLMMA7mmiOR9C3NOKjQ==",
       "dev": true,
       "license": "MIT",
       "dependencies": {