Adds pkg-config plumbing so consumers (daedalus-v4l2 daemon for the
upcoming PR-Q3a shadow-mode wiring; the daedalus_decode_h264 CLI when
built outside this tree) can locate libdaedalus_decoder.a + the public
header via pkg_check_modules / pkg-config.
Mirrors daedalus-fourier's relocatable-prefix scheme: prefix is derived
from ${pcfiledir} so cmake --install --prefix /foo produces a .pc that
resolves to /foo at lookup time. Verified across two install prefixes.
daedalus-fourier is declared as a public Requires: because consumers
static-linking libdaedalus_decoder.a also need libdaedalus_core.a in
their link line to resolve the daedalus_ctx_* / daedalus_recipe_*
symbols this archive references.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
marfrit