Fix cross-compilation of native modules in Dockerfile (#66)

Change builder stage from $BUILDPLATFORM to $TARGETPLATFORM so that
native Node.js modules (better-sqlite3) are compiled for the target
architecture rather than the build machine's architecture.

With $BUILDPLATFORM, cross-compilation scenarios (e.g., arm64 Mac
building for amd64 clusters) produce native binaries for the wrong
architecture, causing runtime failures.

Fixes #65

Signed-off-by: Simon Zhu <simon.zhu@mongodb.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: syn-zhu

mcp/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM --platform=$BUILDPLATFORM cgr.dev/chainguard/wolfi-base:latest AS builder
+FROM --platform=$TARGETPLATFORM cgr.dev/chainguard/wolfi-base:latest AS builder
 
 # Import build arguments for cross-compilation
 ARG BUILDPLATFORM