Initial environment package #1

Ship the first release of @chrismichaelps/pudu-lang-environment: environment files for Pudu that keep a program's secrets out of version control and out of every message the package produces.

Scope:

• The .env format: comments, quoted and multi-line values, escaped quotes, inline comments, export syntax, trimming, and expansion with ${NAME:-default} and ${NAME-default}.
• Given files, upward probing, and a layered environment cascade (.env, .env.local, .env.<name>, .env.<name>.local) with safe environment names.
• Strict and lenient loading, overwrite rules, UTF-8, Latin-1, and UTF-16 sources, and text or byte sources.
• A settled view over the process environment with typed reads, secrets, required keys, and hand-off to child processes.
• Settings records bound by derivation and checked with @chrismichaelps/pudu-lang-validator.

Acceptance:

• Every public module has a suite covering success, failure, edge, and redaction paths.
• pudu check, pudu fmt --check, pudu lint, and pudu test are clean on Pudu 0.1.3.
• Mutation testing of the pure layer kills every valid mutant.
• Runnable examples, README, API documentation in the GitHub Wiki, and a vault page per source file.