fix(tz): split pure helpers out of resolver to keep client bundle clean

`@/lib/tz/resolver` imported `prisma` at module top so any client
component that pulled `detectBrowserTimezone`, `listSupportedTimezones`,
`formatInUserTz`, `userDayKey`, or `DEFAULT_TIMEZONE` dragged
`node:module` into the browser bundle and broke the Turbopack build
(register page, timezone picker, admin general/login sections,
`@/lib/export`).

Pure helpers now live in `@/lib/tz/format` (no Prisma). The resolver
re-exports them so every server-side caller keeps its
`@/lib/tz/resolver` import path; the four client modules + the
export helper now import from `./format` directly.

src/components/admin/general-settings-section.tsx

@@ -4,7 +4,7 @@ import { useMemo } from "react";
 import { Settings } from "lucide-react";
 import { useTranslations } from "@/lib/i18n/context";
 import { SettingsToggle, useAdminSettings, useUpdateSettings } from "./_shared";
-import { listSupportedTimezones } from "@/lib/tz/resolver";
+import { listSupportedTimezones } from "@/lib/tz/format";
 
 const NATIVE_SELECT_CLASS =
   "border-input bg-background text-foreground ring-offset-background focus-visible:ring-ring flex h-9 rounded-md border px-3 py-1 text-sm shadow-xs transition-[color,box-shadow] focus-visible:ring-[3px] focus-visible:outline-none";

src/components/admin/login-overview-section.tsx

@@ -23,7 +23,7 @@ import {
 import { formatDateTime } from "@/lib/format";
 import { useTranslations } from "@/lib/i18n/context";
 import { toCSV } from "@/lib/export";
-import { formatInUserTz, DEFAULT_TIMEZONE } from "@/lib/tz/resolver";
+import { formatInUserTz, DEFAULT_TIMEZONE } from "@/lib/tz/format";
 import { useAuth } from "@/hooks/use-auth";
 import {
   type AdminAuditEntry,