fix(docker): use debian base image for correct MIME types

Alpine lacks shared-mime-info, so file extensions with no built-in Go
mime type (ODF, OOXML, epub, ics, ...) fall back to content sniffing
and are served as "application/zip", breaking Collabora/DAVx5 on
Android. Switch to debian:bookworm-slim and install shared-mime-info.
Also install wget for the /healthz healthcheck instead of curl.

Dockerfile

@@ -10,9 +10,17 @@ RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /bin/davserver ./cmd/s
 RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /bin/nidusctl ./tools/nidusctl
 
 # ---- Runtime stage ----
-FROM alpine:3.19
+FROM debian:bookworm-slim
 
-RUN apk add --no-cache ca-certificates tzdata
+# shared-mime-info: the OS MIME database (/usr/share/mime/globs2) that Go's
+# mime.TypeByExtension consults. Without it, file extensions with no built-in
+# Go type (ODF/.ods, OOXML/.docx, ebook/.epub, calendar/.ics, ...) fall back
+# to content sniffing and are served as "application/zip", which breaks
+# Collabora/DAVx5 on Android. wget: used by the /healthz healthcheck.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+         ca-certificates tzdata wget shared-mime-info \
+    && rm -rf /var/lib/apt/lists/*
 WORKDIR /app
 
 COPY --from=builder /bin/davserver /usr/local/bin/davserver