First Phase F slice. Splits the 1333-LOC `api/subsonic.ts` along its
two most obvious axes:
- `subsonicTypes.ts` — all ~24 exported interfaces + type aliases
(album/song/artist/playlist/directory/genre/now-playing/radio,
random-songs filters, three statistics shapes, search + starred
results, AlbumInfo, structured-lyrics types, etc.) plus the
`RADIO_PAGE_SIZE` constant.
- `subsonicClient.ts` — token-auth + `getClient` + `api<T>()` +
`libraryFilterParams` + `secureRandomSalt` / `getAuthParams` /
`SUBSONIC_CLIENT`. The credential-bearing API helpers
(`pingWithCredentials`, `apiWithCredentials`, `restBaseFromUrl`,
`probeInstantMixWithCredentials`) stay in `subsonic.ts` for now —
they could move into the client module in a follow-up.
66 external call sites migrated to direct imports from the new
modules (no re-export shims in `subsonic.ts`). Pure code-move;
contract test stays green.
subsonic.ts: 1333 → 1078 LOC (−255).
Frank Stellmacher