fix: Drop dotenv package and use native process.loadEnvFile

[Copilot]

Overview

This PR removes the dotenv package dependency and replaces it with Node.js's native process.loadEnvFile() function, which has been available since Node.js 20.12.0.

Motivation

As mentioned in #[issue_number], the dotenv package has started including non-silencable, misleading upselling comments in CLI output that break MCP server functionality. Since Node.js v20 natively supports loading .env files via the process.loadEnvFile() API (introduced in v20.12.0), and this project already requires Node.js >= 20, we can safely migrate to the native implementation.

Changes

Code Changes

• src/bin.js:
  • Removed dotenv import
  • Replaced dotenv.config({ path: filePath }) with process.loadEnvFile(filePath)
  • Added proper error handling to ignore ENOENT errors (file not found), maintaining the same behavior as dotenv
  • Changed the default file path from undefined to ".env" when CROSSPOST_DOTENV=1 (functionally equivalent since dotenv defaults to .env when path is undefined)

Dependency Changes

• package.json: Removed dotenv from dependencies
• package-lock.json: Updated to reflect removal of dotenv package

Documentation Changes

• README.md: Removed link to dotenv package documentation (functionality remains unchanged)

Backward Compatibility

This change is fully backward compatible. The CROSSPOST_DOTENV environment variable continues to work exactly as before:

• CROSSPOST_DOTENV=1 - loads .env from the current working directory
• CROSSPOST_DOTENV=/path/to/file.env - loads the specified .env file
• Non-existent files are silently ignored
• Other errors are properly propagated

Testing

✅ All 298 existing tests pass
✅ Linter passes with no errors
✅ Build completes successfully
✅ Manually verified .env file loading with custom paths
✅ Manually verified non-existent files are handled gracefully
✅ Manually verified CROSSPOST_DOTENV=1 defaults to .env file

Benefits

• Eliminates unwanted console output from dotenv that breaks MCP server
• Reduces package dependencies by 1
• Uses native Node.js functionality, improving maintainability
• Smaller package size

Original prompt

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This section details on the original issue you should resolve

<issue_title>Drop dotenv package</issue_title>
<issue_description>Node supports .env files natively

• with CLI parameter --env-file since 20.6.0
• with API (await process.loadEnvFile('.env');) since 20.12.0

Since v20 is only supported for six more months, and versions before that are already EOL, it might be time to switch to process.loadEnvFile instead of the dotenv package (dreaded because they now include non-silencable, misleading upselling comments in CLI output). I think "they" might have realised that their package has no use in later Node versions.

I don't fully understand the use of dotenv, but it might be time to consider switching to the native integration. </issue_description>

<agent_instructions>Remove the dotenv package and replace it with the native process.loadEnvFile function. See https://codewithhugo.com/load-env-vars-files-nodejs-dotenv/.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@nzakas Sounds like a good idea to me. 👍

Fixes #151

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