fix(packaging): install punktfunk-host on Ubuntu 24.04 LTS via a noble builder that bundles FFmpeg 8

The host .deb was built on the Ubuntu 26.04 rust-ci image, so dpkg-shlibdeps
baked in `Depends: libavcodec62` (FFmpeg 8) and a glibc-2.41 floor — making it
uninstallable on Ubuntu 24.04 LTS (FFmpeg 6.1 / libavcodec60, glibc 2.39; apt
reports the deps as "too recent"). The source floor (ffmpeg-next 8, libavcodec
>=61 APIs) means a straight 24.04 rebuild would fail too.

Build the host on Ubuntu 24.04 instead — lowering the glibc floor to 2.39 so one
binary runs on 24.04 -> 26.04 — and bundle a from-source LGPL FFmpeg 8 into the
package so it no longer depends on the distro libav*. Everything else the host
links is soname-compatible on 24.04 (opus is vendored via cmake; NVENC/libcuda
are dlopen-only, never link-time), and the only FFmpeg encoders used are
*_nvenc / *_vaapi (software H.264 fallback is the BSD-2 openh264 crate, not
FFmpeg libx264), so an LGPL build keeps the bundle license-clean.

- ci/rust-ci-noble.Dockerfile (new): ubuntu:24.04 builder; nv-codec-headers +
  FFmpeg 8 (--enable-nvenc --enable-vaapi, shared) -> /opt/ffmpeg; PKG_CONFIG_PATH.
- packaging/debian/build-deb.sh: BUNDLE_FFMPEG=1 copies libav*/libsw*/libpostproc
  into /usr/lib/punktfunk-host, patchelf-sets the rpath ($ORIGIN per-lib + binary
  --force-rpath), feeds them to dpkg-shlibdeps (captures libva2/libdrm2), and drops
  the libav* sonames from Depends. Normal (non-bundle) path unchanged.
- .gitea/workflows/deb.yml: split into build-publish (client/web/scripting on the
  26.04 image) and build-publish-host (noble image, BUNDLE_FFMPEG=1); parallel,
  identical version step, same apt distribution -> one universal host .deb.
- .gitea/workflows/docker.yml: build+push punktfunk-rust-ci-noble.
- packaging/debian/README.md: document the 24.04 LTS path + bundled local build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/docker.yml

@@ -39,6 +39,12 @@ jobs:
           - image: punktfunk-rust-ci
             dockerfile: ci/rust-ci.Dockerfile
             context: ci
+          # Ubuntu 24.04 LTS host builder: same purpose as rust-ci but lowers the host .deb's glibc
+          # floor to 2.39 and bundles a from-source FFmpeg 8, so the package installs on 24.04 LTS
+          # (rust-ci's 26.04 build is uninstallable there). Consumed by deb.yml's build-publish-host job.
+          - image: punktfunk-rust-ci-noble
+            dockerfile: ci/rust-ci-noble.Dockerfile
+            context: ci
           - image: punktfunk-fedora-rpm
             dockerfile: ci/fedora-rpm.Dockerfile
             context: ci