After a6f529b5, opus_05_51/71 only set endpoint_companion. The owner
fill_caps still advertised up to MAX_CHANNELS, there was no combine_caps,
and validate_config was not id-gated. Disabled surround companions remained
visible in endpoint caps, and SetConfiguration could bind a 5.1/7.1 config
to the stereo opus_05 object (wrong bitrate limits / channel profile).
Mirror a2dp-codec-aac.c:
- split fill_caps per codec id (2ch / 5.1 / 7.1; duplex 2+2; pro wide)
- add combine_caps on endpoint owners
- id-gate validate_config so the config-aware resolver picks the companion
- give companions their own fill_caps for the monitor merge path
a2c09923ff