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/composables/useEnv.ts

@@ -0,0 +1,39 @@
+// Detect which Dezky environment we're running against, from the browser
+// hostname. The env badge in the topbar reads this and uses it as a
+// "you're about to make changes in prod" warning — so it must NOT be
+// user-controllable.
+//
+// Rules:
+//   - hostname ends in `.local` or is `localhost` → 'dev'
+//   - hostname contains `staging` → 'staging'
+//   - anything else → 'prod' (safest default — show the prod styling)
+//
+// SSR returns 'dev' by default because the server has no concept of the
+// browser hostname. The first client tick re-evaluates and the env pill
+// updates without a visible flash for the typical operator workflow
+// (signed-in client-side navigation).
+
+export type Env = 'prod' | 'staging' | 'dev'
+
+function detect(hostname: string): Env {
+  const h = hostname.toLowerCase()
+  if (h === 'localhost' || h === '127.0.0.1' || h.endsWith('.local')) return 'dev'
+  if (h.includes('staging')) return 'staging'
+  return 'prod'
+}
+
+const current = ref<Env>('dev')
+const hostname = ref<string>('')
+let initialized = false
+
+function init() {
+  if (!import.meta.client || initialized) return
+  hostname.value = window.location.hostname
+  current.value = detect(hostname.value)
+  initialized = true
+}
+
+export const useEnv = () => {
+  if (import.meta.client) init()
+  return { env: current, hostname }
+}