Optional email/contact collection step in the widget

[levalex]

Context

Part of a "close the feedback loop" feature: the product needs a way to contact the user after acting on their feedback. When the host app hasn't provided a user identity, the widget should offer to collect an email.

Current state

The widget collects only score / text / choices (src/components/Feedback/Feedback.tsx) plus a Success step. There is no email/contact field.

Expected

• Optional step/field to collect the respondent's email (e.g. after the score/text step, before Success).
• Shown only when contact collection is enabled and no identity was passed in — if a user_id is already provided, don't ask.
• Submitting is optional (the user may skip / not provide it).
• Emit the collected email back through the widget's submit flow so the SDK can send it as attribution.

Wiring (config flag, priority of programmatic user_id) lives on the platform/SDK side; this issue is the widget UI + emitting the value.