feat(webui): rate badges, refresh labels, anchor links

Providers tab (Feature A): a new ProviderRateBadge component renders
each provider's day-window success rate (attempts-failures)/attempts —
always shown when attempts>0 (100% muted, <99% amber via the chart
palette's --color-chart-tokens-out token, <90% destructive, reusing the
Badge component's existing secondary/outline/destructive idioms rather
than inventing a new variant), a distinct "no traffic" badge when
attempts=0, and the live minute-window count in its title attribute.
The same component renders beside a ModelChip inside a provider's
accordion, but only when that model is degraded (<99% with attempts>0)
so a long, healthy model list stays uncluttered. The math and its
threshold constants live in lib/provider-rate.ts, unit-tested directly
(vitest's node environment needs no component mount).

Feature B: a provider's "refreshed ..." label (lib/format.ts's new
refreshLabel) now reads "discovery off" when DiscoveryEnabled is false,
"pending" when it is true but lastRefresh is still unset, and otherwise
the unchanged relative-time text — replacing the misleading "refreshed
never" a discovery-disabled provider showed before.

Feature C: composables/useTabHash syncs App.vue's active tab to the URL
hash (#providers/#usage/#charts/#targets, matching the existing
TabsTrigger values) with no router dependency. On load it reads the
current hash (falling back to "providers" for an absent or invalid one);
on tab change it writes the hash back via history.replaceState (no
scroll jump, no new history entry per click); a hashchange listener
handles back/forward and hand-edited URLs. hashToTab/tabToHash are
exported as pure functions so the mapping is unit-tested directly,
independent of window/history/location — every DOM touch inside
useTabHash itself is guarded behind one hasWindow check so the module
still imports cleanly under vitest's node test environment.
AuthGate never reads or writes the hash, so a tab named in the URL
survives the unauthenticated -> authenticated transition unchanged.

webui/src/lib/format.spec.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest'
+
+import { refreshLabel } from './format'
+
+const ZERO_TIME = '0001-01-01T00:00:00Z'
+
+describe('refreshLabel', () => {
+  it('reads "discovery off" when discovery is disabled, regardless of lastRefresh', () => {
+    expect(refreshLabel(false, ZERO_TIME)).toBe('discovery off')
+    expect(refreshLabel(false, new Date().toISOString())).toBe('discovery off')
+    expect(refreshLabel(false, undefined)).toBe('discovery off')
+  })
+
+  it('reads "pending" when discovery is enabled but lastRefresh is still the unset sentinel', () => {
+    expect(refreshLabel(true, ZERO_TIME)).toBe('pending')
+  })
+
+  it('reads "pending" when discovery is enabled and lastRefresh is undefined (edge case)', () => {
+    expect(refreshLabel(true, undefined)).toBe('pending')
+  })
+
+  it('reads the relative-time "refreshed (Ns ago)" text once discovery has completed a refresh', () => {
+    const oneMinuteAgo = new Date(Date.now() - 60_000).toISOString()
+    expect(refreshLabel(true, oneMinuteAgo)).toMatch(/^refreshed \(\d+s ago\)$/)
+  })
+})