hubspot: region selection (EU portals via js-eu1.hs-scripts.com)

[productdevbook]

EU customers need `js-eu1.hs-scripts.com`; wrappers default to US.

Evidence

• `Allow European configuration aaronhayes/react-use-hubspot-form#44` — "Allow European configuration" Allow European configuration aaronhayes/react-use-hubspot-form#44

Tasks

• `load({ portalId, region: "na1" | "eu1" })`
• Auto-detect by `portalId` range is not possible, always require explicit
• Default `na1`, document EU flag prominently for GDPR guidance

[productdevbook]

Implemented in this commit