refactor(frontend): split hooks/ into shared, scanner, admin (Phase 5)

[revtex]

Summary

Phase 5 of the directory restructure plan. Pure file moves with import-path updates and new barrel index files; no runtime behaviour change.

File moves (15 files, all tracked as renames)

hooks/shared/

• useAuthInit.ts (+ .test.tsx)
• useTheme.ts
• useTokenRefresh.ts (+ .test.tsx)
• useWebSocket.ts

hooks/scanner/

• useScanner.ts
• useAudioPlayer.ts
• useTGSelectionSync.ts
• useActiveUnit.ts

hooks/admin/

• useAdminWebSocket.ts
• useAdminWsOps.ts
• useAdminActivity.ts
• useAdminLogs.ts
• useWsQuery.ts

New barrel files

Added index.ts in each subfolder plus a root hooks/index.ts as a safety net. Per the plan, callers should prefer specific paths (@/hooks/shared/useTheme); the root barrel is only there as a fallback.

Import updates

All 31 @/hooks/* import sites across components, pages, intra-hook references, and test vi.mock calls have been updated to specific paths.

Verification

• pnpm exec tsc --noEmit — clean
• pnpm test -- --run — 188/188 pass
• Pre-existing eslint error in services/downloadFilename.ts is unchanged from dev (out of scope)

Phase progress

• Phase 0 — Pre-flight cleanup
• Phase 1 — /api/ws canonical + /ws alias
• Phase 2 — internal/admin extraction
• Phase 3 — internal/api decomposition (refactor(backend): Phase 3 — decompose internal/api into feature-scoped handler packages #18)
• Phase 4 — Frontend services reorg (refactor(frontend): group services into services/ws and services/audio (Phase 4) #20)
• Phase 5 — Frontend hooks reorg (this PR)
• Phase 6 — Frontend types split (pause-and-review checkpoint after this one)
• Phase 7 — (Optional) migrations path move

CHANGELOG

One bullet appended under [Unreleased] ### Changed.