feat(setup): allow alternative context key instead of 'web'

[Ibochkarev]

What does it do?

Adds support for specifying a custom web context key during MODX installation instead of the default web. Changes include:

• CLI installer (cli-install.php): New context_web_key prompt with validation (alphanumeric + underscore, forbids mgr and root)
• Web installer (contexts.php, contexts.tpl): New input field for context key with validation and error display
• Config (modinstallrunner.class.php): New writeContextConfig() method that writes config.context.php to the web root with the chosen context key
• Database (new.install.php): When a custom key is used, renames the web context and updates related tables (modContextSetting, modContextResource, modAccessContext, modResource)
• Default settings (modinstallrequest, modinstallclirequest): context_web_key defaults to web

The index.php already reads config.context.php when present (fallback to web if missing).

Why is it needed?

Allows users to install MODX with a custom front-end context key (e.g. site, frontend) instead of requiring web. Useful for multi-site setups, security through obscurity, or naming conventions.

How to test

CLI install:

php setup/cli-install.php --context_web_key=site
# Or: php setup/cli-install.php (prompt will ask for context key, default: web)

Web install:

1. Run setup wizard
2. On the contexts step, enter a custom key (e.g. site) in the "Web context key" field
3. Complete installation
4. Verify config.context.php exists in web root with return 'site';
5. Verify site loads with the custom context

Validation:

• Empty key → fallback to web
• Invalid chars (e.g. site-key) → error on web, fallback on CLI
• Reserved keys (mgr, root) → error on web, fallback on CLI

Related issue(s)/PR(s)

Resolves #14462