Major repository cleanup and enhancement

- Reorganize documentation: moved old docs to docs/ directory
- Add comprehensive README.md with build options and usage guide
- Add detailed CONTRIBUTING.md with help content management guide
- Create Makefile for automated building and testing
- Add Dockerfile.scratch for building from Ubuntu 20.04 base
- Enhance all Dockerfiles with PowerShell + PSScriptAnalyzer
- Add modern shells: zsh (with plugins) and fish (with config)
- Add modern CLI tools: fd-find, ripgrep, fzf
- Create comprehensive help system with cheat/TLDR/fish completions
- Add helper scripts for help content management and coverage checking
- Fix Dockerfile.remnux script references
- Support three build variants: upstream (REMnux), scratch (Ubuntu), kali

Build options:
  - make build-upstream: Fast, uses REMnux upstream (recommended)
  - make build-scratch: Full control, builds from Ubuntu 20.04
  - make build-kali: Legacy Kali Linux base

Features:
  - PowerShell with PSScriptAnalyzer module
  - Modern shells (zsh, fish) with custom configurations
  - Enhanced help system (cheat sheets, TLDR pages, fish completions)
  - Help coverage checking and bulk import tools
  - Comprehensive documentation for users and contributors

docs/remnux-dockerfile-focal.txt

@@ -0,0 +1,53 @@
+# This Docker image encapsulates the REMnux v7 distro on Ubuntu 20.04 (focal).
+# For details about REMnux, including how you can run it on a physical system
+# or as a virtual machine, see https://REMnux.org.
+#
+# You can run this image as a container using a command such as:
+#
+# docker run --rm -it remnux/remnux-distro /bin/bash
+#
+# To map a local directory into the container's /home/remnux/files directory,
+# you could use a command lile this by supplying the appropriate directory name:
+#
+# docker run --rm -it -v <local_directory>:/home/remnux/files remnux/remnux-distro /bin/bash
+#
+# If you'd like to access the container using SSH,  you can invoke it like this by
+# mapping your local TCP port 22 to the container's internal TCP port 22. In this example,
+# the container will remain active in the background:
+#
+# docker run -d -p 22:22 remnux/remnux-distro
+#
+# If you're going to run this container in a remote cloud, be sure to change the default
+# password and otherwise harden the system according to your requirements.
+#
+# If you're planning to use Cutter inside the container, you'll need to include the
+# --privileged parameter when invoking Docker.
+#
+
+FROM ubuntu:20.04
+
+LABEL description="REMnux® is a Linux toolkit for reverse-engineering and analyzing malicious software."
+LABEL maintainer="Lenny Zeltser (@lennyzeltser, zeltser.com)"
+LABEL version="v2025.30.1"
+ARG CAST_VER=0.16.22
+
+USER root
+
+WORKDIR /tmp
+RUN export DEBIAN_FRONTEND=noninteractive && \
+    apt-get update && \
+    apt-get install -y wget gnupg git && \
+    wget https://github.com/ekristen/cast/releases/download/v${CAST_VER}/cast-v${CAST_VER}-linux-amd64.deb && \
+    dpkg -i /tmp/cast-v${CAST_VER}-linux-amd64.deb && \
+    cast install --mode cloud --user remnux remnux && \
+    rm -rf /root/.cache/* && \
+    unset DEBIAN_FRONTEND
+
+RUN rm /tmp/cast-v${CAST_VER}-linux-amd64.deb
+
+ENV TERM=linux
+WORKDIR /home/remnux
+
+RUN mkdir /var/run/sshd
+EXPOSE 22
+CMD ["/usr/sbin/sshd", "-D"]