fix(admin): share the zero-time constant

The zero-time sentinel was module private, so the spec redeclared the
literal once a third consumer started depending on it. Export it and
import it in the spec. Regenerate the baked admin assets.

Claude-Session: https://claude.ai/code/session_01EebV5jyWvYocByNQ3oss1w

webui/src/lib/format.spec.ts

@@ -1,8 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { formatCompactCount, formatContextWindow, formatElapsedAgo, formatLatencyMs, formatModelCostHover, formatUntil, refreshDetailLabel, refreshLabel } from './format'
-
-const ZERO_TIME = '0001-01-01T00:00:00Z'
+import { formatCompactCount, formatContextWindow, formatElapsedAgo, formatLatencyMs, formatModelCostHover, formatUntil, refreshDetailLabel, refreshLabel, ZERO_TIME } from './format'
 
 describe('refreshLabel', () => {
   it('reads "discovery off" when discovery is disabled, regardless of lastRefresh', () => {

webui/src/lib/format.ts

@@ -1,6 +1,7 @@
 import type { HistoryWindow, LimitsConfig } from '@/types/api'
 
-const ZERO_TIME = '0001-01-01T00:00:00Z'
+/** ZERO_TIME is Go's zero time.Time value in its default JSON (RFC 3339) encoding — the unset-timestamp sentinel every admin API "never happened yet" field marshals as, and every formatter/test below treats as absent. */
+export const ZERO_TIME = '0001-01-01T00:00:00Z'
 
 /**
  * routableModelId joins a provider name and one of its own model ids into