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

files/zshrc

@@ -0,0 +1,39 @@
+# REMnux File Analysis Container - ZSH Configuration
+
+# History
+HISTFILE=~/.zsh_history
+HISTSIZE=10000
+SAVEHIST=10000
+setopt SHARE_HISTORY HIST_IGNORE_ALL_DUPS HIST_FIND_NO_DUPS HIST_REDUCE_BLANKS
+
+# Navigation
+setopt AUTO_CD AUTO_PUSHD PUSHD_IGNORE_DUPS PUSHD_SILENT
+
+# Completion
+autoload -Uz compinit && compinit
+zstyle ':completion:*' menu select
+zstyle ':completion:*' matcher-list 'm:{a-zA-Z}={A-Za-z}'
+setopt COMPLETE_IN_WORD AUTO_MENU
+
+# Load plugins
+[[ -f /usr/share/zsh-autosuggestions/zsh-autosuggestions.zsh ]] && \
+    source /usr/share/zsh-autosuggestions/zsh-autosuggestions.zsh
+[[ -f /usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh ]] && \
+    source /usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
+
+# Prompt
+autoload -U colors && colors
+PROMPT='%F{cyan}remnux%f@%F{blue}%m%f:%F{yellow}%~%f%# '
+RPROMPT='%F{green}[%D{%H:%M:%S}]%f'
+
+# Aliases
+alias ls='ls --color=auto'
+alias ll='ls -lah'
+alias grep='grep --color=auto'
+alias fd='fdfind'
+alias rg='rg --color=auto'
+alias analyse='fhelp'
+alias ?='fhelp'
+
+# Welcome
+[[ -f /opt/README ]] && cat /opt/README && echo "" && echo "🐚 Shell: zsh | Type 'fhelp' for help" && echo ""