v9.15.0 — Common taxonomies catalog (toggles + onboarding)

Ships the code for the common-taxonomies feature documented earlier under the v9.13.0 heading — that entry was committed without its implementation and no v9.13.0 tag was cut, so v9.15.0 is the first release that actually contains it (github:CaspianTools/script-caspian-store#v9.15.0).

A broad, categorized catalog of common product taxonomies — Brands, Seasons, Occasions, Trends, Materials, Colors, Sizes, Patterns, Fit, Gender, Age group, Care instructions, Country of origin, Certifications — grouped into Merchandising / Attributes / Audience / Care & origin.

Admins enable/disable them on a new Settings → Taxonomies sub-page (toggle a whole category or a single one) and during the /setup onboarding wizard (new dedicated step). Only enabled taxonomies show in the Catalog → Taxonomies sidebar — no empty pages. A taxonomy that already has terms can't be disabled (the toggle locks on; guarded by a live `getCountFromServer` count, re-checked at toggle-off time).

Generic taxonomies share one `taxonomyTerms` collection keyed by a `type` field, with a single generic CRUD page (`AdminTaxonomyTermsPage`); Brands stays bespoke. The enabled set persists as `SiteSettings.enabledTaxonomies` (defaults to Brands when unset). Includes a `taxonomy-terms` import/export descriptor.

No consumer action required

Additive. `SiteSettings.enabledTaxonomies` is optional and defaults to Brands; the new `taxonomyTerms` collection is public-read/admin-write like the other product taxonomies (deploy `firestore.rules` to use generic taxonomies). No composite index needed (equality-only queries). The setup wizard gains a Taxonomies step automatically.

Install: `github:CaspianTools/script-caspian-store#v9.15.0`