add multistore support with mage add store and mage add stores

[allrude]

Adds interactive and batch workflows for creating Magento 2 store views under a Valet local development environment.

New commands:
mage add store — interactive: prompts for code, name, domain, locale;
creates the store view via dev/tools/create-store.php,
sets base URLs, updates .valet-env.php, and runs
valet link + valet secure in one step.
mage add stores — batch: reads dev/tools/stores.json and creates all
defined store views non-interactively; batches all
valet link calls then all valet secure calls to avoid
redundant nginx restarts.

stores.json schema (project-agnostic — domain derived from project name):
{
"stores": [
{ "code": "nl_nl", "name": "Dutch", "suffix": "nl", "locale": "nl_NL" }
]
}

Changes:
src/_multistore.sh (new)
- mage_valet_env_add_entry: appends a store entry to .valet-env.php using Python 3; skips duplicates safely.
- mage_add_store: single-store interactive flow with auto-lowercase of store code and input validation.
- mage_add_stores_from_file: batch flow; resolves stores.json from dev/tools/ -> project root -> mage bin dir; computes domain as - so stores.json is project-agnostic.

src/_setup.sh
- Removed hardcoded placeholder store-2 / default2 from mage_setup.
- mage_setup now scaffolds dev/tools/create-store.php and dev/tools/stores.json from the mage bin directory into every new project automatically.
- After scaffold, mage_setup prompts to run mage_add_stores_from_file if stores.json is non-empty (skippable with N).

src/_info.sh — added help entries for add store and add stores
src/_mage.sh — added dispatch cases for add store and add stores

[GrimLink]

Closing for f15f0c4

While this is the same in function as the one in the PR, it does lack the json based setup option, seeing this outside the scope of the logic and would be beter handled when building the #38