Customizing's first consumer (partner catalogs)

The Customizing engine's first real consumer, plus the i18n tooling that pairs with it.

Added

• Partner-role + relationship-type catalogs are now code-owned Customizing — the first real consumer of the engine. New Partners\Attributes\PartnerRole + Partners\Attributes\RelationshipType (both CustomizingEntry, distinct from the existing Partners\Models\*), Partners\Enums\PartnerRoleCode + Partners\Enums\RelationshipTypeCode, and the SDK-generic baseline declared on PartnersModule: 9 roles (supplier/employee/department/cost_center + bill_to/ship_to/payer/approver/project_lead) and 2 relationship types (employed_by, owns). They land in sdk_partner_roles / sdk_partner_relationship_types on ui5:sync — every install gets the baseline for free, no host seeding. Lifecycle codes (lead/prospect/customer/churned, …) remain host-specific.
• ui5:i18n command — expands the i18n keys for the synced Customizing catalogs into a base .properties bundle (customizing.<catalog>.<code>.<column>, seeded with the source-language literal). Base-only (never a localized *_<locale>.properties — that's the translators' domain) and append-only (safe to re-run; never duplicates or overwrites a refined label). --out sets the target (default resources/ui5/i18n/db.properties, a refresh-safe bundle so ui5:app --refresh can't clobber it). v1 covers the Customizing family; the cross-cutting expansion of Roles / Settings / Act / Access is the documented next step.