test(ui): isolate full chat-pane lifecycle tests to fix core-runtime-media-ui flake (#112566)

The core-runtime-media-ui shard runs its ui config non-isolated for speed, but the
full chat-pane lifecycle tests instantiate the pane component, which relies on
chat-thread/chat-message module-level singletons (thread-state map, confirmation
dismisser WeakMap, module-scoped document context-menu listeners) and spies on those
modules. Under the shared non-isolated graph a stateful predecessor file can leave
those modules duplicated, so the pane binds to a different instance than the test's
spy/registry -- producing order-dependent flakes: `removeEventListener`-not-called
teardown assertions or 120s session-lifecycle hangs. Reproduced deterministically on
a Linux Node 24 Testbox (MAX_WORKERS=1); isolating a single file only shifted the
failure to a sibling pane test, so the whole full-pane family shares the fragility.

Route the 7 full-pane lifecycle test files through a new isolated jsdom lane
(vitest.ui-isolated.config.ts, isolate: true) for a fresh module graph; the other
~370 ui tests stay fast and non-isolated. Registered in both shard registries
(ci-node-test-plan.mjs, vitest.test-shards.mjs) and excluded from vitest.ui.config.ts.

Verified on Testbox: the deterministic single-worker media-ui shard goes from failing
to 5182 passed / 0 failed. Test-infrastructure only; no product code changes.

test/scripts/ci-node-test-plan.test.ts

@@ -664,6 +664,7 @@ describe("scripts/lib/ci-node-test-plan.mjs", () => {
           "test/vitest/vitest.media-understanding.config.ts",
           "test/vitest/vitest.tui.config.ts",
           "test/vitest/vitest.ui.config.ts",
+          "test/vitest/vitest.ui-isolated.config.ts",
           "test/vitest/vitest.wizard.config.ts",
         ],
         requiresDist: false,

test/scripts/test-projects.test.ts

@@ -4731,6 +4731,7 @@ describe("scripts/test-projects full-suite sharding", () => {
       "test/vitest/vitest.tui.config.ts",
       "test/vitest/vitest.tui-pty.config.ts",
       "test/vitest/vitest.ui.config.ts",
+      "test/vitest/vitest.ui-isolated.config.ts",
       "test/vitest/vitest.utils.config.ts",
       "test/vitest/vitest.wizard.config.ts",
       "test/vitest/vitest.gateway-core.config.ts",