Add AGENTS.md (comprehensive agent guide)

Mainly generated by codex-cli v0.39.0, with gpt-5-codex high, and this
AGENTS.md construction prompt:
- https://gist.github.com/PeterDaveHello/f30c38a156982a35683edfd5ece2d474

Reference:
- https://agents.md/

Co-authored-by: qodo-merge-for-open-source[bot] <189517486+qodo-merge-for-open-source[bot]@users.noreply.github.com>

Author: PeterDaveHello

AGENTS.md

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+# Repository Guidelines
+
+## Dos and Don'ts
+
+- **Do** regenerate the distribution scripts with `./generator.sh` whenever you touch `generator.sh` or `color table.txt`; commit the resulting `dist/ColorEcho.*` updates together.
+- **Do** run targeted checks (`shellcheck`, `shfmt`, `./test-scripts/<shell>`) only on the files you touched to keep diffs focused; the CI pipeline still runs the full matrix.
+- **Do** honor the 2-space indentation defined in `.editorconfig` for shell and Markdown files.
+- **Don't** edit the files under `dist/` by hand; they are generated output and will be overwritten by `./generator.sh`.
+- **Don't** mass-format or rewrite unrelated scripts; align with the existing naming and function structure produced by the generator.
+
+## Project Structure and Module Organization
+
+ColorEchoForShell ships colorized `echo` helpers for multiple shells.
+
+- `dist/ColorEcho.{bash,sh,ksh,zsh,fish}`: generated shell-specific helpers; source this directory in user scripts.
+- `generator.sh`: builds the contents of `dist/`; relies on `color table.txt` for color codes.
+- `color table.txt`: canonical mapping of color names to ANSI codes.
+- `test-scripts/<shell>`: runtime smoke tests that source the matching dist file and exercise every function.
+- `.travis.yml`: Travis CI pipeline defining the canonical lint, format, and runtime test matrix.
+- `.editorconfig`, `.markdownlint.json`: repository formatting and Markdown lint rules.
+- `README.md`, `Demo.*`: project overview and assets.
+
+## Build, Test, and Development Commands
+
+All commands assume the repository root as the working directory.
+
+- Regenerate distribution scripts: `./generator.sh`
+- Run ShellCheck on touched files, e.g. `shellcheck generator.sh`, `shellcheck dist/ColorEcho.sh`, `shellcheck dist/ColorEcho.ksh`, or `shellcheck dist/ColorEcho.bash`
+- Format updated shell scripts with the CI image: `docker run -it --rm -v "$(pwd)":/sh -w /sh peterdavehello/shfmt:3.3.0 shfmt -sr -i 2 -ci -w generator.sh` (replace `generator.sh` with any touched source files). Keep the `peterdavehello/shfmt:3.3.0` tag aligned with `.travis.yml`.
+- Lint Markdown with the CI image: `docker run -it --rm -v "$(pwd)":/md peterdavehello/markdownlint markdownlint '**/*.md'`
+- Validate dist output in bash: `./test-scripts/bash` (replace `bash` with `sh`, `ksh`, `zsh`, or `fish` for other shells)
+
+Install `echint` (`npm install -g echint`) to mirror the CI `.editorconfig` check and run `echint`.
+
+## Coding Style and Naming Conventions
+
+- Shell and Markdown files use 2-space indentation, UTF-8, and trimmed trailing whitespace per `.editorconfig`.
+- Keep function and file names consistent with the generator output (`echo.<Style><Color>`); new helpers must be added through `generator.sh`.
+- Comments and user-facing text are written in en-US; match the concise style in `dist/ColorEcho.*`.
+- When formatting shell scripts, rely on `shfmt` with `-sr -i 2 -ci` to stay aligned with CI.
+
+## Testing Guidelines
+
+- Use the scripts under `test-scripts/` to exercise the generated output for the corresponding shell; they exit on first failure.
+- Prefer running only the variants impacted by your changes (e.g., run `./test-scripts/ksh` after updating `generator.sh` in a way that affects the ksh output).
+- Runtime tests depend on the availability of each shell binary; install the shell locally if it is missing.
+- If you modify color definitions or generator logic, rerun all shell variants to ensure parity.
+
+## Commit and Pull Request Guidelines
+
+- Follow the prevailing style: imperative, capitalized subjects without trailing periods (e.g., `Add markdownlint test on Travis CI`), optional descriptive body wrapped at 72 chars.
+- Keep commits focused, commit generated `dist/` changes with their source updates, and ensure all configured checks in `.travis.yml` pass.
+- Reference related issues or PRs in the body when relevant and note environment prerequisites for reviewers.
+
+## Safety and Permissions
+
+- Ask before adding dependencies, deleting files, or altering CI configuration; keep edits scoped to the problem at hand.
+- Do not run destructive commands or rename generated files; rely on `generator.sh` for updates.
+- You may freely read files, run targeted linters/tests, and create small patches; confirm large or cross-cutting changes with the maintainer.
+- Exclude secrets or environment-specific data from commits and documentation.