`invokeAudioSetNormalizationDeduped` (450 ms window for
`audio_set_normalization`) and `invokeAudioUpdateReplayGainDeduped`
(250 ms window for `audio_update_replay_gain`, with LUFS-target /
pre-trim implicitly contributing to the dedupe key) move into
`src/store/normalizationIpcDedupe.ts` along with their four
"last-invoked" mutables.
File-private throughout; three internal call sites become plain
imports. 11 focused tests cover the window-boundary behaviour, the
payload-field sensitivity, the engine-mode key contribution
(re-fires when LUFS target changes even with identical gain), and
the null / NaN serialization.
playerStore 3369 → 3302 LOC.
Frank Stellmacher