feat(audio): v1 signature producer, bit-exact with the pipeline

`AudioSignature` is the DSP — band table, periodic Hann, radix-2 FFT,
band-mean peak, energy class, packing — and `AudioSignatureService` the
decode, running the FFmpeg binary `IMediaEncoder.EncoderPath` names. The
plugin gained no dependency.

The server specification's prose does not determine a byte stream, so the
parameters it leaves open are pinned by the fixture shared with the
extraction repo and restated at the top of `AudioSignature`: double
throughout, whole frames only, periodic Hann, unnormalised FFT, band mean
rather than sum, argmax ties to the lowest index.

`fixtures/audio/` holds the extraction repo's three files byte-identically
and the computed signature equals the recorded vector exactly. The binding
check regenerates the fixture PCM from `make_fixture.py`'s arithmetic and
verifies it against the recorded decode checksums, so it runs on a host
with no codec at all and a decode divergence stays distinguishable from a
DSP one; the two tests that drive real FFmpeg self-skip without a binary.

The workflow named "Test Plugin" until now only compiled one. A test that
is built and never run is not evidence, and a golden vector shared across
two repos exists precisely so CI fails when they drift.

TRACES: JR-042, JR-043 | SR-003

.gitea/workflows/test.yaml

@@ -42,6 +42,16 @@ jobs:
         working-directory: test-${{ github.run_id }}
         run: dotnet build Jellyfin.Plugin.JRay.sln --configuration Debug --no-restore --no-self-contained /m:1
 
+      # The workflow is named "Test Plugin" and until now only compiled one. A
+      # test that is built but never run is not evidence, and JR-043 is the case
+      # that makes it matter: the point of a golden vector shared with the
+      # extraction repo is that CI fails when the two implementations drift.
+      # T1 needs no ASP.NET runtime and no FFmpeg — the audio golden check
+      # regenerates its own fixture PCM.
+      - name: Run tests
+        working-directory: test-${{ github.run_id }}
+        run: dotnet test Jellyfin.Plugin.JRay.sln --configuration Debug --no-restore --no-build
+
       - name: Cleanup
         if: always()
         run: rm -rf test-${{ github.run_id }}