feat(api): SHA-256 and Chromaprint fingerprints for the library (M5.5)

A background Fingerprinter runs after every scan and at startup, one file
at a time, filling media_files.sha256 and track_fingerprints (fpcalc raw,
first 120 s). Without fpcalc only SHA-256 is computed and files stay
queued for Chromaprint. Changing a file's content resets its prints.
Similarity() compares raw prints with a ±80-point alignment search; it is
the basis for duplicate detection in the upload queue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/api/Dockerfile

@@ -14,9 +14,9 @@ RUN --mount=type=cache,target=/go/pkg/mod --mount=type=cache,target=/root/.cache
     go build -trimpath -ldflags "-s -w -X pipu/api/internal/buildinfo.Version=${VERSION}" -o /out/api ./cmd/api && \
     go build -trimpath -ldflags "-s -w -X pipu/api/internal/buildinfo.Version=${VERSION}" -o /out/storage-agent ./cmd/storage-agent
 
-# api вызывает ffprobe (сканер) и ffmpeg (транскодинг, M3) — нужен не distroless, а alpine с ffmpeg.
+# api вызывает ffprobe (сканер), ffmpeg (транскодинг, M3) и fpcalc (отпечатки, M5.5) — нужен не distroless, а alpine.
 FROM alpine:3.22 AS api
-RUN apk add --no-cache ffmpeg ca-certificates tzdata
+RUN apk add --no-cache ffmpeg chromaprint ca-certificates tzdata
 COPY --from=build /out/api /usr/local/bin/api
 USER 65532:65532
 EXPOSE 8080