Linux/macOS now follow the local-build path in CI and CD:
tooling/install-deps.sh installs the distro codec packages and
tooling/ffmpeg/build-ffmpeg.sh builds the pinned static FFmpeg into
.cache/ffmpeg, with FFMPEG_DIR/PKG_CONFIG_PATH pointing there. CI caches
the built tree keyed on the script, distro and arch (the
.build-complete marker rejects partial saves); CD rebuilds it from
scratch per its no-cache policy. Windows keeps BtbN's prebuilt shared
archive, downloaded from the release page and verified against its
checksums.sha256 — no pkg-config is needed there any more.
vcpkg.json, the release-only overlay triplets and the x264 mirror
overlay are deleted; docs/build.md describes the new flow.
Mike-Solar
563a3625ca