fix: use npm to install pnpm in Dockerfile

Replace corepack with npm install for pnpm installation
to avoid signature verification issues in Docker build.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: harryisfish

docker/Dockerfile

@@ -6,10 +6,11 @@ RUN apk update --no-cache && apk add --no-cache \
     pixman-dev \
     cairo-dev \
     pango-dev \
-    pkgconfig
+    pkgconfig \
+    curl
 
-# Install pnpm
-RUN corepack enable && corepack prepare pnpm@latest --activate
+# Install pnpm using npm (more reliable than corepack in Docker)
+RUN npm install -g pnpm@latest
 
 COPY . /app
 WORKDIR /app