fix(webui): resilient dashboard polling (SF7)

useDashboardStore.refresh() used Promise.all across overview/usage/
targets: one route rejecting threw before any of the three state
fields were assigned, so a single flaky GET /admin/api/targets blanked
the already-working Providers and Usage views too.

Switched to Promise.allSettled with per-section assignment: a
fulfilled result updates its own field, a rejected one leaves the
PREVIOUS value in place rather than nulling it. lastUpdated still
advances on a partial success (some fresh data did arrive); error
names which section(s) failed. A 401/403 on any section still defers
to the auth store exactly as before (AdminApiError check unchanged).

Added dashboard.spec.ts — the first Pinia store under vitest in this
package (a store needs no DOM, so it fits the existing 'node'
environment without pulling in jsdom); vite.config.ts's own test-scope
comment updated to say so.

webui/vite.config.ts

@@ -33,12 +33,16 @@ export default defineConfig({
     modulePreload: { polyfill: false },
   },
   test: {
-    // Deliberately narrow: only lib/'s pure modules (search-expand.ts,
-    // usage-search.ts) are under vitest right now (webui's test infra
-    // starts here, on purpose — no snapshot/DOM/component testing this
-    // round). 'node' is enough since neither module touches browser
-    // globals; jsdom is not pulled in as a dependency for modules that
-    // don't need it.
+    // Deliberately narrow: lib/'s pure modules (search-expand.ts,
+    // usage-search.ts) plus, since review round 2 (v0.21), stores/
+    // dashboard.ts's own refresh() action — a Pinia store is plain
+    // reactive state and actions, no DOM or component mount involved, so
+    // it fits this same environment. Still no snapshot/DOM/component
+    // (.vue mount) testing. 'node' is enough since nothing under test
+    // touches a real browser global — dashboard.spec.ts mocks lib/api.ts
+    // entirely, so even sessionStorage access (auth.ts) never actually
+    // runs; jsdom is not pulled in as a dependency for modules that don't
+    // need it.
     environment: 'node',
     include: ['src/**/*.spec.ts'],
   },