Add dev container configuration

[lpcox]

No description provided.

[Copilot]

Pull request overview

Adds a VS Code Dev Container setup to standardize local development for MCP Gateway contributors and make it easier to run/build/lint/test inside a containerized environment.

Changes:

• Introduces .devcontainer/devcontainer.json with Go-focused VS Code settings, extensions, and port forwarding.
• Adds a .devcontainer/Dockerfile to build a Go 1.25-based dev image, install tooling, and warm the Go module cache.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.devcontainer/devcontainer.json	Defines the devcontainer build, features (DinD, GitHub CLI), VS Code settings/extensions, and forwarded ports.
.devcontainer/Dockerfile	Builds the devcontainer image, installs golangci-lint and common CLI tools, and pre-downloads Go modules.

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[Copilot]

The devcontainer installs golangci-lint by piping a script from the master branch of an external repo into sh. This is not reproducible and increases supply-chain risk (the script contents can change without any version bump). Prefer downloading a specific released artifact (or pinning the installer script to a commit) and verifying checksums/signatures so the devcontainer build is deterministic.

Suggested change

	RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh \
	| sh -s -- -b /usr/local/bin ${GOLANGCI_LINT_VERSION}
	ARG GOLANGCI_LINT_CHECKSUM=REPLACE_WITH_SHA256_FOR_v2_8_0_LINUX_AMD64
	RUN set -eux; \
	arch="$(uname -m)"; \
	case "$arch" in \
	x86_64) golangci_arch="amd64" ;; \
	aarch64) golangci_arch="arm64" ;; \
	*) echo "Unsupported architecture: $arch" >&2; exit 1 ;; \
	esac; \
	version="${GOLANGCI_LINT_VERSION#v}"; \
	url="https://github.com/golangci/golangci-lint/releases/download/${GOLANGCI_LINT_VERSION}/golangci-lint-${version}-linux-${golangci_arch}.tar.gz"; \
	curl -sSfL "$url" -o /tmp/golangci-lint.tar.gz; \
	echo "${GOLANGCI_LINT_CHECKSUM} /tmp/golangci-lint.tar.gz" | sha256sum -c -; \
	tar -xzf /tmp/golangci-lint.tar.gz -C /tmp; \
	mv "/tmp/golangci-lint-${version}-linux-${golangci_arch}/golangci-lint" /usr/local/bin/; \
	rm -rf /tmp/golangci-lint*