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

python_helpers/env.py

@@ -0,0 +1,33 @@
+"""Environment file helpers for command-line scripts."""
+
+import os
+
+from python_helpers.console import fail
+
+
+def load_env_file(path):
+    """Load a docker-style environment file into the process environment.
+
+    Blank lines and lines whose first non-blank character is # are ignored; a # anywhere
+    else is part of the value. A NAME=VALUE line sets the variable, overriding any value
+    already in the environment; a bare NAME line leaves the inherited value in place.
+    Values are taken literally, without quote removal or variable interpolation. An empty
+    name, or one containing whitespace, is an error.
+
+    Args:
+        path: path to the environment file.
+    """
+    try:
+        with open(path, encoding="utf-8") as env_file:
+            lines = env_file.read().splitlines()
+    except OSError as error:
+        fail(f"Could not read '{path}': {error}")
+
+    for number, line in enumerate(lines, start=1):
+        if not line.strip() or line.lstrip().startswith("#"):
+            continue
+        name, separator, value = line.partition("=")
+        if not name or any(character.isspace() for character in name):
+            fail(f"{path}: line {number}: variable '{name}' is empty or contains whitespace")
+        if separator:
+            os.environ[name] = value