Fix hyperhdrAdjust: use "brightness", not "scaleOutput"

Tested against a real HyperHDR instance rather than trusting the
schema further. scaleOutput (from the current schema-adjustment.json)
produced no visible change and no trace in serverinfo's echoed-back
adjustment state. brightness (0-100, absent from that same schema)
round-tripped correctly through serverinfo and visibly dimmed real
LEDs -- confirmed live, with piccap as the sole colour source and
only this sink's JSON-RPC calls changing anything.

A schema documents what a command accepts; it does not guarantee
what a given build actually does with each field, and this is a
mismatch between HyperHDR's current dev-branch schema and whatever
build the target instance is actually running. Switched the sink to
brightness (int 0-100) throughout: wire format, config defaults
(minBrightness/maxBrightness, 20-100), status fields, and the reset
sent on close. Renamed the frontend fields and mock to match.
Cross-compiles clean. Bumped to 1.0.4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/js/mock.js

@@ -16,7 +16,7 @@
       mode: 'spectrum', saturation: 1.0, minBrightness: 0.02,
     },
     hyperhdrAdjust: {
-      host: '', port: 19444, minScale: 0.3, maxScale: 1.3, level: 'rms',
+      host: '', port: 19444, minBrightness: 20, maxBrightness: 100, level: 'rms',
     },
     udp: { host: '', port: 4010, multicastTtl: 4 },
     tcp: { port: 4011, maxClients: 4 },