refactor(lib): consolidate generic infra into src/lib

Move domain-agnostic, feature-free helpers out of the flat utils/ and store/
roots into src/lib/ (plan M4, §3 lib/ layer):
- lib/format/: formatBytes, formatClockTime, formatDuration, formatHumanDuration,
  relativeTime (pure format/date/byte/clock helpers)
- lib/i18n.ts: i18next bootstrap (global app infra)
- lib/util/: sanitizeHtml, platform, dedupeById, safeStorage (pure helpers +
  the zustand storage adapter)

playbackScheduleFormat stays in utils/format (runtime usePlayerStore dep =
audio-core coupling, not generic). formatClockTime keeps a type-only
@/store/authStoreTypes import (erased, no runtime inversion — accepted per the
deviceSync precedent).

Pure move via deep @/lib/* specifiers (no barrel → no mock-collapse surface).
tsc 0, lint 0/0, full suite 319 files / 2353 tests green.

Tooling note: lib_move.py regex extended to also rewrite side-effect imports
(import './i18n') and vi.importActual paths — both were silent gaps.

src/features/settings/components/ThemeStoreSection.tsx

@@ -6,7 +6,7 @@ import CoverLightbox from '@/components/CoverLightbox';
 import { useThemeAnimationRisk } from '@/hooks/useThemeAnimationRisk';
 import { AnimatedThemeBadge } from '@/features/settings/components/AnimatedThemeBadge';
 import CustomSelect from '@/ui/CustomSelect';
-import { formatRelativeTime } from '@/utils/format/relativeTime';
+import { formatRelativeTime } from '@/lib/format/relativeTime';
 import { useThemeStore } from '@/store/themeStore';
 import { useInstalledThemesStore, type InstalledTheme } from '@/store/installedThemesStore';
 import {