refactor(network): decouple network-reachability layer from features → lib/network

The connection-reachability + Subsonic network-guard helpers were pinned low by
four lib/api consumers (subsonicLibrary/Playlists/Ratings/Scrobble) yet ran two
lower-layer→feature inversions. Both removed without a registry:

- devOfflineBrowseStore is a self-contained DEV-only toggle with zero offline-
  feature coupling — it was only colocated there. Relocated features/offline/store
  → store/ (global). The @/features/offline barrel re-exports it so feature/UI
  consumers are unchanged; the three lower-layer readers (subsonicNetworkGuard,
  activeServerReachability, useConnectionStatus) now import it from @/store directly.

- subsonicNetworkGuard's only other feature dep was playback's resolvePlaybackUrl,
  used solely for the psysonic-local:// skip check. Added hasLocalPlaybackUrl to the
  existing M4 substrate store/localPlaybackResolve — it mirrors resolvePlaybackUrl's
  local-source branch exactly (same profile resolution; the empty-serverId playback
  fallback never applies in the guard), so the skip stays bit-identical.

network/ (subsonicNetworkGuard + activeServerReachability + tests) → lib/network,
now @/features-free. useConnectionStatus is now iron-rule-clean and stays in hooks/
(cross-cutting). Test mocks retargeted to the new seam modules.

Behavior-adjacent (covered by suite; default paths identical): the local-bytes skip
helper — flag for offline-playback runtime QA alongside the M4 media-resolver seam.

src/features/playback/store/b1QueueServerIdentity.test.ts

@@ -37,7 +37,7 @@ vi.mock('@/lib/api/subsonicPlayQueue', () => ({
   savePlayQueue: vi.fn(async () => undefined),
   getPlayQueue: vi.fn(async () => ({ songs: [], current: undefined, position: 0 })),
 }));
-vi.mock('@/utils/network/activeServerReachability', () => ({
+vi.mock('@/lib/network/activeServerReachability', () => ({
   isActiveServerReachable: () => true,
 }));
 

src/features/playback/store/playerStore.persistence.test.ts

@@ -30,7 +30,7 @@ vi.mock('@/lib/api/subsonicPlayQueue', () => ({
   savePlayQueue: vi.fn(async () => undefined),
   getPlayQueue: vi.fn(async () => ({ songs: [], current: undefined, position: 0 })),
 }));
-vi.mock('@/utils/network/activeServerReachability', () => ({
+vi.mock('@/lib/network/activeServerReachability', () => ({
   isActiveServerReachable: () => true,
 }));
 vi.mock('@/lib/api/subsonicStreamUrl', () => ({

src/features/playback/store/queueSync.test.ts

@@ -13,7 +13,7 @@ const { savePlayQueueMock, playerState, progressSnapshot, isSubsonicServerReacha
 }));
 
 vi.mock('@/lib/api/subsonicPlayQueue', () => ({ savePlayQueue: savePlayQueueMock }));
-vi.mock('@/utils/network/subsonicNetworkGuard', () => ({
+vi.mock('@/lib/network/subsonicNetworkGuard', () => ({
   isSubsonicServerReachable: (serverId: string) => isSubsonicServerReachableMock(serverId),
 }));
 vi.mock('@/features/playback/utils/playback/playbackServer', () => ({

src/features/playback/store/queueSync.ts

@@ -1,6 +1,6 @@
 import { savePlayQueue } from '@/lib/api/subsonicPlayQueue';
 import type { QueueItemRef, Track } from '@/lib/media/trackTypes';
-import { isSubsonicServerReachable } from '@/utils/network/subsonicNetworkGuard';
+import { isSubsonicServerReachable } from '@/lib/network/subsonicNetworkGuard';
 import {
   filterQueueRefsForPlaybackServer,
   getPlaybackServerId,