fix(docker): add multi-arch (amd64/arm64) Docker build support

[MuhammadAbeerAkmal]

Problem: The nmrkit Docker image only works on amd64 machines right now. It doesn't run on arm64 machines, like Apple Silicon Mac (M2) etc. houdini69 on #110 ran into this issue and just want nmrkit to work on his machine.

What change in this PR:

• Dockerfile: JAVA_HOME is hardcoded to .../java-17-openjdk-amd64/, which would silently point at a non-existent path when built for arm64 (Debian installs the arm64 JDK under .../java-17-openjdk-arm64/). Added ARG TARGETARCH and switched the path to use it, so it resolves correctly per architecture.
• dev-build.yml / prod-build.yml: added a docker/setup-qemu-action@v3 step (needed so GitHub's amd64 runners can emulate arm64 during the build) and platforms: linux/amd64,linux/arm64 on the main nmrkit image build step.

Testing: Verified the Dockerfile still builds locally for amd64. Haven't been able to test the arm64 build itself locally which will need to run in CI.

@NishaSharma14: New to this repo! It would be nice if you please review it.

[Copilot]

Pull request overview

Adds multi-architecture (amd64/arm64) Docker build support so nmrkit can run on arm64 hosts (e.g., Apple Silicon) by removing an amd64-specific JAVA_HOME assumption and enabling multi-platform builds in CI.

Changes:

• Parameterize JAVA_HOME in the Dockerfile using TARGETARCH for per-arch JDK install paths.
• Enable QEMU emulation and request linux/amd64,linux/arm64 builds in the dev and prod GitHub Actions workflows.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
Dockerfile	Switches JAVA_HOME to an architecture-dependent path using TARGETARCH.
.github/workflows/dev-build.yml	Adds QEMU setup and enables multi-platform builds for the main image.
.github/workflows/prod-build.yml	Adds QEMU setup and enables multi-platform builds for the main image.

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[NishaSharma14]

@MuhammadAbeerAkmal Thank you for your pull request. Can you please check the review comments by Copilot and check if they are relevant to be resolved?

[MuhammadAbeerAkmal]

@NishaSharma14 I checked all four Copilot comments and they were relevant. Added a safe default for TARGETARCH, removed a dead export line, and confirmed Microsoft's Playwright base image does support arm64, so I extended multi-arch support to nmr-cli too rather than leaving it out of scope. Ready for review whenever you get a chance.