feat: dotenv (.env)

[tianzhou]

Also expand ENV support

Fix #25

[Copilot]

Pull Request Overview

This PR adds dotenv (.env) file support to pgschema, allowing users to configure database connection parameters through environment variables and .env files. The changes expand environment variable support for standard PostgreSQL environment variables like PGHOST, PGPORT, PGDATABASE, PGUSER, PGPASSWORD, and PGAPPNAME.

Key changes include:

• Added godotenv library integration to automatically load .env files
• Created utility functions for environment variable handling with defaults
• Updated all CLI commands to support PostgreSQL environment variables
• Added comprehensive documentation and examples for dotenv usage

Reviewed Changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
main.go	Loads .env file on application startup using godotenv
cmd/util/env.go	New utility functions for environment variable handling
cmd/*/cmd.go	Updated command flag definitions to use environment variables
docs/cli/*.mdx	Updated documentation to include environment variable references
docs/cli/dotenv.mdx	New comprehensive documentation for dotenv feature
.env.example	Example .env file template for users

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