refactor(webui): rename Overview tab to Providers

Mechanical rename: OverviewView.vue -> ProvidersView.vue (file, component
import, tab label/value in App.vue), plus doc-comment/README references
across webui/ that named the view by its old tab label.

The backend GET /admin/api/overview endpoint, adminOverviewResponse type,
and the frontend AdminOverviewResponse/dashboard.overview field all keep
their original names unchanged (API surface) -- only the UI tab label and
the component/file that renders it changed. No behavior or layout change
to the view itself.

webui/src/composables/useSearchQuery.ts

@@ -2,12 +2,12 @@ import { computed, ref } from 'vue'
 
 /**
  * useSearchQuery is the one raw-query → {normalized, hasQuery} adapter
- * every search filter in this panel uses — OverviewView's model search,
+ * every search filter in this panel uses — ProvidersView's model search,
  * UsageView's user/group search, ChartsView's scope-picker search all had
  * their own copy of this identical query/normalizedQuery/hasQuery
  * pairing; extracted so it exists once (vue.md: "if you've written it
  * twice, you owe an abstraction"). Callers still own their own matching
- * logic entirely (OverviewView's modelMatches/providerMatches,
+ * logic entirely (ProvidersView's modelMatches/providerMatches,
  * lib/usage-search.ts's helpers) — this only normalizes the raw input the
  * same way every call site already agreed on: trimmed, lowercased.
  *