own-host page: an LV2 URI through omx-clap-host, run in CI on Debian bookworm and trixie (#52)

[linuxnow]

What: docs/own-host.md gets an LV2 section (a second block, eight commands): quit the first daemon, install omx-plugins-lv2, write a config file with lv2_worker omx-clap-host, start the daemon, add lv2:urn:openmixer:comp 0, set and read back the Ratio by its LV2 symbol, and check worker_list names the lv2-clap worker. The "what we still need" bullet about LV2 now says what is left (a plugin the adapter refuses needs mod-host, which no Debian or channel package carries).

CI: the existing own-host-page job (bookworm and trixie, amd64 and arm64) now runs both blocks as one script through tests/own_host_page.py, with the reader checks of both blocks in its selftest. With --audio it then sets the compressor to Ratio 1 and Makeup 6 dB and runs tests/own_host_lv2_probe.py, which uses python3 and libjack only: it plays a 0.25 sine into effect_0 and measures the peak at the outputs. The step passes only when out/in is 1.9953 +- 0.03 on both channels, so a value measured from audio that went through the LV2 plugin in omx-clap-host, not an exit code.

Tested: selftest (make check-own-host-page) passes, 9 + 8 commands, and each of the nine wrong replies stops the script. The full page plus audio step run in clean debian:trixie and debian:bookworm containers on this amd64 host against the published channel (daemon 0.4.0, worker and plugins 0.10.0): gain 1.9953 on both. Sabotage: makeup 0 instead of 6 in the audio step gave gain 1.0000 and the step failed; restored. arm64 is untested here (no arm64 host); CI runs it natively.

Refs #52