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
      <project-name>-<suffix> 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`