ci(rpm): publish punktfunk-host RPM to the Gitea registry (Bazzite)

Mirrors the apt pipeline for Fedora Atomic / Bazzite. New `rpm` workflow builds
the host RPM in a Fedora 43 builder image (ci/fedora-rpm.Dockerfile — matches
Bazzite's libavcodec.so.61, with a self-contained 16-symbol libcuda link stub so
no NVIDIA packages are needed in CI) and uploads to Gitea's public RPM registry
(group "bazzite") on every main push (rolling 0.0.1-0.ciN.<sha>) and v* tag
(clean X.Y.Z-1). Bazzite hosts then track it with `rpm-ostree upgrade`.

- packaging/rpm/build-rpm.sh: git-archive tarball + rpmbuild (--nodeps, since the
  toolchain is rustup + dnf, not RPMs); copies to dist/, asserts no cuda/nvidia leak.
- punktfunk.spec: overridable pf_version/pf_release for CI snapshots; exclude
  libcuda.so from auto-Requires (NVENC/EGL come from the driver, out of band) —
  same NVIDIA filter as the .deb; fix a bogus changelog weekday.
- docker.yml builds+pushes the new fedora-rpm image; packaging README + rpm/README
  document the rpm-ostree install/update path (recommended option).

Builder image seeded to the registry so rpm.yml's first run finds it. RPM build +
clean-Requires verified locally in the image (libavcodec.so.61 / libavutil.so.59,
no cuda).

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

.gitea/workflows/docker.yml

@@ -2,6 +2,7 @@
 #   punktfunk-web      — management console (web/Dockerfile, repo-root context)
 #   punktfunk-docs     — documentation site (docs-site/Dockerfile)
 #   punktfunk-rust-ci  — Rust CI builder image consumed by ci.yml
+#   punktfunk-fedora-rpm — Fedora 43 builder image consumed by rpm.yml (Bazzite RPM)
 # Host and clients are intentionally NOT containerized (see CLAUDE.md "What's left").
 #
 # REGISTRY_TOKEN: repo Actions secret, a PAT with write:package scope.
@@ -38,6 +39,9 @@ jobs:
           - image: punktfunk-rust-ci
             dockerfile: ci/rust-ci.Dockerfile
             context: ci
+          - image: punktfunk-fedora-rpm
+            dockerfile: ci/fedora-rpm.Dockerfile
+            context: ci
     steps:
       - uses: actions/checkout@v4