Add initial implementation of Python helpers and CLI tools

- Create .gitignore to exclude build artifacts
- Add README.md with project description and installation instructions
- Implement pyproject.toml for package metadata and script entry points
- Add console output helpers for command-line scripts
- Implement environment file loading functionality
- Add JSON file I/O helpers
- Create token decoder CLI for decoding JWT claims
- Implement serve-markdown CLI for serving Markdown files as HTML

README.md

@@ -0,0 +1,82 @@
+# Python Helpers
+
+Generic Python helpers and command-line tools with no cloud-specific logic. It has no external
+dependencies.
+
+- `serve-markdown`: serve Markdown files as live-reloading GitHub-styled HTML pages
+- `token-decoder`: decode a JWT's claims without verifying its signature
+
+## Installation
+
+Each command below is available on `PATH` directly (no `.py` extension, no `python3` prefix)
+once the package is installed into the active virtual environment, by any of the methods below.
+
+### Local install
+
+From a checkout of this repository:
+
+```bash
+pip install -e .   # editable, for development: picks up source changes without reinstalling
+pip install .      # normal install: copies the package in
+```
+
+### Install from git
+
+```bash
+pip install git+<repository-url>@main
+```
+
+### Running without installing
+
+From a repo checkout, run any command as a module with `-m` instead of installing the package:
+
+```bash
+python3 -m python_helpers.cli.token_decoder --help
+```
+
+From elsewhere, set `PYTHONPATH` to the repo root instead:
+
+```bash
+PYTHONPATH=/path/to/python-helpers python3 -m python_helpers.cli.token_decoder --help
+```
+
+The module path replaces the installed command's short hyphenated name; the underlying `main()`
+and behavior are identical.
+
+## Library
+
+- `console`: colored console output and the `fail()` helper used to report errors and exit
+- `env`: loading docker-style `NAME=VALUE` environment files into the process environment
+- `files`: JSON file load/save helpers
+
+## Commands
+
+### `token-decoder`
+
+Decode a JWT's claims, without verifying its signature. Reads from a file argument, or stdin.
+
+Example:
+
+```bash
+token-decoder token.txt
+echo "$TOKEN" | token-decoder
+```
+
+### `serve-markdown`
+
+Render Markdown files under a directory as GitHub-styled pages and serve them locally, live-reloading
+on change.
+
+Parameters:
+
+- `path` (optional, positional): Markdown file or directory to serve; defaults to the current directory. A directory is served at its own URL path, resolving to `index.md` or `README.md` within it. Prefix with `pydoc:` and a dotted module name (e.g. `pydoc:python_helpers.console`) to render that module's docs with `pydoc-markdown` instead; requires the `pydoc-markdown` package to be installed
+- `--listen-address` (optional): Address for the local web server to listen on (default: `127.0.0.1`)
+- `--port` (optional): Port for the local web server (default: `8000`)
+- `--watch-interval` (optional): Seconds between checks for changes to the file, polled by the browser page (default: `1.0`)
+
+Example:
+
+```bash
+serve-markdown README.md
+serve-markdown pydoc:python_helpers.console
+```