Add read.sh for displaying system prompt files

[Copilot]

Shell utility to read/display the system prompt files in this repo.

• read.sh: Lists, reads individual, or dumps all prompt files (--list, --all, <file>)
• README.md: Documents usage

./read.sh --list                        # list available prompts
./read.sh claude-system-prompt.txt      # read one
./read.sh --all                         # read all

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