feat(webui): add limit bars, forecasts, events, exports and URL state

The Usage tab shows a bar for each configured limit. It turns amber at
80% and red at 100%. The tab also shows rejected requests per day, a
projected month-end cost with budget headroom, and CSV export for users
and groups. Names link to Charts with the matching scope.

The Charts tab ranks models over the full 24h, 30d or 12mo window. A
provider filter is applied on the server, and the ranking can be
exported as CSV. A new Events tab lists recent failures, filtered by
kind and user. The selected tab, filters and scope live in the URL
hash. Polling stops while the page is hidden. Views show which replica
answered, and a banner lists configuration warnings.

CSV cells that start with a formula character are neutralised. Links
sit outside the accordion buttons, so both controls keep their
accessible names. admin_assets_gen.go is regenerated.

Claude-Session: https://claude.ai/code/session_01V5jYJNxpDFdJkyyExpADrv

webui/src/stores/dashboard.ts

@@ -1,6 +1,7 @@
 import { defineStore } from 'pinia'
 
 import { AdminApiError, adminFetch } from '@/lib/api'
+import { createVisibilityPoller, type VisibilityPoller } from '@/lib/polling'
 import { useAuthStore } from '@/stores/auth'
 import type { AdminOverviewResponse, AdminTargetsResponse, AdminUsageResponse } from '@/types/api'
 
@@ -24,7 +25,7 @@ export const useDashboardStore = defineStore('dashboard', {
     targets: null as AdminTargetsResponse | null,
     lastUpdated: null as Date | null,
     error: '',
-    timer: undefined as ReturnType<typeof setInterval> | undefined,
+    poller: undefined as VisibilityPoller | undefined,
     /**
      * refreshing guards against overlapping polls (review finding): the 5s
      * setInterval has no in-flight check on its own, so a round trip that
@@ -95,11 +96,26 @@ export const useDashboardStore = defineStore('dashboard', {
         .map(({ label, reason }) => `${label}: ${reason instanceof Error ? reason.message : String(reason)}`)
         .join('; ')
     },
-    /** startPolling is idempotent and safe to call before a key is stored — refresh() no-ops until then. */
+    /**
+     * startPolling is idempotent and safe to call before a key is stored —
+     * refresh() no-ops until then. Driven by the shared
+     * createVisibilityPoller (lib/polling.ts, F5) rather than a bare
+     * setInterval: an immediate tick (the same "fetch once, then poll"
+     * shape this action already had), then every POLL_MS while the tab is
+     * visible, pausing while it is hidden and catching up the moment it is
+     * looked at again.
+     */
     startPolling(): void {
-      if (this.timer !== undefined) return
-      void this.refresh()
-      this.timer = setInterval(() => void this.refresh(), POLL_MS)
+      if (this.poller) return
+      this.poller = createVisibilityPoller({ intervalMs: POLL_MS, tick: () => void this.refresh() })
+      this.poller.start()
     },
+    // P11 review fix: a stopPolling action mirroring history.ts/events.ts's
+    // own stop() used to live here too, but nothing outside its OWN spec
+    // ever called it — App.vue mounts this store's poller once, for the
+    // app's whole session, and never unmounts it (unlike history.ts/
+    // events.ts, whose stores are torn down when ChartsView/EventsView
+    // unmount). Dead application-facing API surface, removed; `poller`
+    // itself stays (startPolling's own idempotency guard still needs it).
   },
 })