[Docs/Feature] cli: support global configuration file

[gslvly]

Problem

Currently, playwright-cli only supports project-level configuration via .playwright/cli.config.json. There's no documented way to set global configuration that applies across all projects.

For example, I want to always use --extension mode to connect to my browser, but I have to specify it every time:

playwright-cli --extension open https://example.com

Proposed Solution

Support a global configuration file, similar to how many CLI tools work:

1. ~/.playwright/cli.config.json - user-level global config
2. .playwright/cli.config.json - project-level config (current behavior)

Project config could override/merge with global config.

Example global config:

{
  "extension": true
}

This would make playwright-cli open automatically use --extension mode.

Alternative

Document environment variable PLAYWRIGHT_MCP_EXTENSION=true as a way to set global defaults, similar to other PLAYWRIGHT_MCP_* environment variables already documented.

Current Workaround

Using shell alias:

alias playwright-cli='playwright-cli --extension'

But this doesn't work well for coding agents that spawn new processes without loading shell config.

References

The README mentions:

• Project config: .playwright/cli.config.json
• Environment variables: PLAYWRIGHT_MCP_*

But there's no clear guidance on setting persistent global defaults.

[laurentpayot]

That would be super useful 👍