fix: use musl build tag for go-fitz on Alpine (musl libc)

Dockerfile

@@ -14,7 +14,7 @@ ENV GOSUMDB=off
 RUN sed -i 's|https://dl-cdn.alpinelinux.org|https://mirrors.aliyun.com|g' /etc/apk/repositories && \
     apk add --no-cache gcc musl-dev && \
     go mod download && \
-    CGO_ENABLED=1 GOOS=linux go build -ldflags="-s -w" -o doc_ai ./main.go
+    CGO_ENABLED=1 GOOS=linux go build -tags musl -ldflags="-s -w" -o doc_ai ./main.go
 
 # Runtime stage
 FROM crpi-8s2ierii2xan4klg.cn-beijing.personal.cr.aliyuncs.com/texpixel/alpine:latest