Add Docker support for Linux build testing

- Introduced a `Dockerfile` for setting up a minimal Ubuntu-based build environment with required dependencies.
- Added `docker-build.sh` script to simplify Linux build and test execution using Docker or Podman.
- Updated `DEVELOPER_GUIDE.md` with instructions for using Docker/Podman for Linux builds, including CI/CD integration examples.

Dockerfile

@@ -0,0 +1,20 @@
+# Minimal Dockerfile for building and testing kte on Linux
+# This container provides a build environment with all dependencies.
+# Mount the source tree at /kte when running the container.
+FROM ubuntu:22.04
+
+# Avoid interactive prompts during package installation
+ENV DEBIAN_FRONTEND=noninteractive
+
+# Install build dependencies
+RUN apt-get update && apt-get install -y \
+    build-essential \
+    cmake \
+    libncursesw5-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Set working directory where source will be mounted
+WORKDIR /kte
+
+# Default command: build and run tests
+CMD ["sh", "-c", "cmake -B build -DBUILD_GUI=OFF -DBUILD_TESTS=ON && cmake --build build --target kte && cmake --build build --target kte_tests && ./build/kte_tests"]