Add host-tools/setup.sh to create .env with prompts

[iarif4u]

Part of #257 (the first idea: set up .env with prompts instead of vim). The one-step run script is in #346 for #260.

Purpose

Hosts say that the runner install is tedious. Today, they clone the repo, copy .env.default, edit it in vim, and find out on the first run whether the database credentials work. This script does those steps and checks them.

What host-tools/setup.sh does

1. Checks the software: php git rsync wget unzip node npm. composer is optional. It prints the Node.js and npm versions and stops with a list if something is missing.
2. Asks for the values: database name, user, password, host, PHP executable, checkout directory, and the report API key. Passwords and the API key are not shown when you type them. Press Enter to keep the current value.
3. Tests the database connection with the runner's own wpt_runner_parse_db_host() and mysqli, using WPT_PHP_EXECUTABLE. If the connection fails, .env is not changed.
4. Writes .env from .env.default. It changes only the lines it asks about. It quotes each value safely, sets the file mode to 600, and saves the old .env as .env.bak-<timestamp>.

Also:

• Sets WPT_TEST_DIR to WPT_PREPARE_DIR. With .env.default as it is, the two are different (wp-test-runner and /tmp/wp-test-runner), so a local run stops in check_required_env() with "WPT_TEST_DIR must be the same as WPT_PREPARE_DIR".
• --non-interactive takes the values from the environment, for provisioning tools. --skip-checks and --skip-db-check skip those steps.
• Warns when run as root.
• It does not install software, create the database, or set up cron. Those are different for each host.

The README "Configuring the Runner" section now mentions the script first, before the manual steps.

Testing

Tested against a real MySQL 9.6 server with PHP 8.4:

Case	Result
--non-interactive, correct credentials	Connects, writes .env (mode 600), exit 0
source .env, then check_required_env()	Passes
Wrong password	"Access denied", .env unchanged, exit 1
Invalid WPT_DB_HOST	"WPT_DB_HOST is not valid", .env unchanged
Interactive, values with ', #, $ and spaces	Values are the same after source .env
Run again, Enter for every value	Keeps the values, saves a backup
Environment value set	Environment value wins over the current .env
node, npm or wget missing	Lists the missing software, exit 1

Contributed at WordCamp Contributor Day.

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