build: add Dockerfile + VS code dev container configuration

Adds Dockerfile to provide a container running Debian with all
required packages installed to build and run mecaps demo application.

Adds devcontainer.json so that Dockerfile can be used as
dev container in VS code.

Tested on Debian 12 running X11 with:
- VS code version 1.89.1
- Docker version 26.1.3 (running as rootless)
  https://docs.docker.com/engine/security/rootless/

.devcontainer/devcontainer.json

@@ -0,0 +1,30 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/docker-existing-dockerfile
+{
+	"name": "MECAPS Dockerfile",
+	"build": {
+		// Sets the run context to one level up instead of the .devcontainer folder.
+		"context": "..",
+		"dockerfile": "../Dockerfile"
+	},
+
+	// Mount X11 UDS directory to allow for running GUIs from inside the container
+	"mounts": [ "source=/tmp/.X11-unix/,target=/tmp/.X11-unix/,type=bind" ],
+	// Set DISPLAY environment variable non-statically (using `remoteEnv` instead of `containerEnv`)
+	"remoteEnv": { "DISPLAY": "${localEnv:DISPLAY}" },
+
+	// Optional: Setup VNC (requires complementary config in Dockerfile to be enabled also)
+	// "forwardPorts": [5900], // default VNC server port
+
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"llvm-vs-code-extensions.vscode-clangd",
+				"ms-vscode.cmake-tools",
+                "ms-vscode.cpptools",
+				"Slint.slint",
+				"vadimcn.vscode-lldb"
+			]
+		}
+	}
+}

Dockerfile

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+FROM debian:bookworm-slim
+
+RUN apt-get update --quiet && \
+    apt-get install --assume-yes \
+    # minimal build essentials
+    cmake \
+    curl \
+    g++ \
+    git \
+    ninja-build \
+    wget \
+    # mecaps / kdutils specific pkgs
+    libcurlpp-dev \
+    libmosquittopp-dev \
+    libwayland-dev \
+    wayland-scanner++ \
+    wayland-protocols \
+    # slint specific pkgs
+    libfontconfig-dev \
+    libxcb-shape0-dev \
+    libxcb-xfixes0-dev \
+    libxcb-xkb-dev \
+    libxkbcommon-dev \
+    libxkbcommon-x11-dev \
+    qtbase5-dev
+
+# Install slint from binary
+ARG SLINT_VERSION=1.6.0
+ENV SLINT_INSTALL_DIR=/usr/src/slint
+WORKDIR $SLINT_INSTALL_DIR
+RUN wget --quiet -O - https://github.com/slint-ui/slint/releases/download/v$SLINT_VERSION/Slint-cpp-$SLINT_VERSION-Linux-x86_64.tar.gz | tar xvzf - --strip-components=1
+
+# Set CMake prefix path
+ENV CMAKE_PREFIX_PATH=$SLINT_INSTALL_DIR
+
+# Optional: Setup VNC (requires complementary config in devcontainer.json to be enabled also)
+# (Configures slint to use Qt backend and sets Qt Platform Plugin to VNC)
+# ENV SLINT_BACKEND=qt
+# ENV QT_QPA_PLATFORM=vnc