perf-audio deprioritized Pulsar to nice 10 in cool/extreme and nice 5 in
standard, on the theory that the editor should yield to audio. That trade buys
nothing. The entire audio chain runs SCHED_FIFO *above* it — scsynth 90,
sclang 85, PipeWire 95, WirePlumber 95, Ardour 80 — and a realtime policy
preempts every CFS nice level unconditionally. So Pulsar at -5 cannot take a
single cycle from SuperDirt; it only wins against ordinary processes (browsers,
indexers, builds), which is exactly what we want during a composing session.

Now nice -5 in every mode, overridable with PULSAR_NICE=NN (0 = neutral,
positive = the old behaviour). -5 rather than 0 because the renderer is a single
JS thread and its work is bursty: it has to win the CPU on the tick after a
keystroke, then yield. No root needed — @audio's `nice -19` grant in
/etc/security/limits.conf is what makes the same renice work for pln.

Validated: installed to /usr/local/sbin/perf-audio, re-applied via
`bridge.py perf standard`, all Pulsar processes confirmed at nice -5 live.