refactor(frontend): split types/index.ts into topic-scoped modules (Phase 6)

[revtex]

Summary

Phase 6 of the directory restructure plan. The 413-line types/index.ts god-file is split into seven topic-scoped modules; the original path becomes a barrel that re-exports everything so all existing @/types import sites continue to compile unchanged.

New layout

File	Contents
types/call.ts	Call, TranscriptionSegment
types/config.ts	SystemConfig, TalkgroupConfig, ScannerConfig
types/ws.ts	WsCommand, ConnectionStatus
types/auth.ts	LoginResponse, RefreshResponse, ChangePasswordRequest
types/api.ts	SetupStatus
types/admin.ts	All Admin* DTOs, Capabilities, ConfigResponse, CreateUserPayload, UpdateUserPayload, RR* enrichment, SharedLinkAdmin, ServerDirectory*, transcription DTOs
types/ui.ts	AvoidEntry
types/index.ts	barrel re-export of all of the above

No type signatures or behaviour changed. No call-site imports needed updating because the barrel covers the existing @/types surface.

Verification

• pnpm exec tsc --noEmit — clean
• pnpm test -- --run — 188/188 pass

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 (refactor(frontend): split hooks/ into shared, scanner, admin (Phase 5) #21)
• Phase 6 — Frontend types split (this PR) — pause-and-review checkpoint
• Phase 7 — (Optional) migrations path move

After this merges, only the optional Phase 7 (move backend/migrations/ → backend/db/migrations/) remains.

CHANGELOG

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