Run test-suite on PRs via GitHub Actions; retire Travis

[Copilot]

Wire up CI so the meson test-suite builds and runs on every PR, with all GStreamer/codec dependencies (x264, libav, voaac, speex) provisioned on the runner. The previous Travis config predates the current test-suite and is no longer used.

Changes

• .github/workflows/ci.yml (already present on this branch) builds and runs the suite on pull_request, pushes to master, and workflow_dispatch. Installs the full dependency set on ubuntu-latest, then meson setup -Dtests=enabled → meson compile → meson test, uploading meson-logs/ as an artifact on all outcomes.
  • Added a concurrency group to cancel superseded runs on the same ref.
• Removed .travis.yml — superseded by the Actions workflow.

Dependency notes

The codecs the harness instantiates map onto stock apt packages; no separate x264 package is required:

Element	Package
x264enc	gstreamer1.0-plugins-ugly
avdec_h264, avdec_aac	gstreamer1.0-libav
voaacenc, aacparse, h264parse	gstreamer1.0-plugins-bad
speexenc/speexdec (optional coverage)	gstreamer1.0-plugins-good

To enable

CI activates once this lands on the default branch. To gate merges, add a branch-protection rule requiring the build-and-test check. Fork PRs need the standard first-run maintainer approval; no secrets are used (workflow is contents: read only).