refactor(operator): derive env badge from hostname, not from user choice

A toggle-able env badge is a sticker, not a safety signal. Move env to
useEnv() which reads window.location.hostname:
  *.local / localhost → 'dev'
  *staging* → 'staging'
  everything else → 'prod' (safest default)

- New composable: apps/operator/composables/useEnv.ts
- Topbar reads useEnv() instead of useTweaks().env
- useTweaks loses the env field; hydrate strips it from stale
  localStorage payloads so old entries don't break
- TweaksPanel: env section removed (theme + density remain)
- Settings: env section removed from Appearance; added a read-only
  Environment row to the Profile card showing the detected env +
  hostname source ("auto-detected from operator.dezky.local")

apps/operator/components/OpTopbar.vue

@@ -1,16 +1,14 @@
 <script setup lang="ts">
 withDefaults(defineProps<{ oncall?: boolean }>(), { oncall: true })
 
-const { state: tweaks } = useTweaks()
 const { open: openPalette } = useCommandPalette()
+const { env } = useEnv()
 
 const ENVS = {
   prod:    { label: 'PROD',    fg: 'var(--text)', bg: 'rgba(244,243,238,0.08)', border: 'rgba(244,243,238,0.15)' },
   staging: { label: 'STAGING', fg: '#FFC872',     bg: 'rgba(232,154,31,0.16)',  border: 'rgba(232,154,31,0.36)' },
   dev:     { label: 'DEV',     fg: '#D4AAFF',     bg: 'rgba(159,98,212,0.18)',  border: 'rgba(159,98,212,0.36)' },
 } as const
-
-const env = computed(() => tweaks.value.env)
 </script>
 
 <template>