feat: add tenant domain model and update static YAML catalog

[RawanMatar89]

Summary

Adds the Tenant domain model and TenantsConfig container that later multi-tenant PRs build on. Inert — nothing in the app calls it yet.

Included

• Tenant / TenantsConfig (Core): per-tenant API/SSO/OAuth fields, UI feature-flag overrides, raw branding fields (color, logoURLString, themeColors) for a later theming PR to render
• UIComponentsConfig → @unchecked Sendable (required so Tenant can hold one as a stored property)
• config.yaml TENANTS: block — one placeholder tenant, not real data

Not included

• Remote catalog fetch, TenantStore selection/session state, anything reading TenantProvider — separate PRs
• JSON parsing path in TenantsConfig.swift (stops at its own // MARK: Remote (JSON) parsing boundary)

Testing

Built and ran successfully on device.

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Note

This is the first pull-request of the multi-tenant infrastructure extraction.

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