Filter Template meta-filter: reference existing PP templates inside others
for composable, DRY filter chains. Filters are recursively expanded at
pipeline build time with cycle detection. New `select` option type with
dynamic choices populated by the API.
Keepalive optimization: serial devices (Adalight, AmbiLED) don't need
keepalive — they hold last frame indefinitely. Check `standby_required`
capability at processor start, skip keepalive sends for serial targets,
and hide keepalive metrics in the UI. Rename "Standby Interval" to
"Keep Alive Interval" throughout the frontend.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
alexei.dolgolyov
9e555cef2e