chore: add devcontainer config and additional packages for ddev

.devcontainer/devcontainer.json

@@ -0,0 +1,14 @@
+// For format details, see https://aka.ms/devcontainer.json.
+{
+	"name": "ddev-claude-cli",
+	"image": "mcr.microsoft.com/devcontainers/go:2-1.27-bookworm",
+	"features": {
+		"ghcr.io/anthropics/devcontainer-features/claude-code:1.0": {},
+		// DDEV needs a Docker daemon; this runs one inside the devcontainer.
+		"ghcr.io/devcontainers/features/docker-in-docker:2": {},
+		// Official DDEV feature: installs ddev (and mkcert) for testing the add-on end to end.
+		"ghcr.io/ddev/ddev/install-ddev:latest": {}
+	},
+	// ShellCheck for the add-on's bash scripts; bats + helpers are what the DDEV add-on template's tests use.
+	"postCreateCommand": "sudo apt-get update && sudo apt-get install -y --no-install-recommends shellcheck bats bats-assert bats-support bats-file"
+}