Q&A response notification — notify workflow initiator when answer arrives

[aselim31]

Problem

When a respondent submits an answer via MagicLink or web form, the response flows back via QuestionnaireService (#632) but nothing notifies the workflow initiator that the loop has closed. The initiator either polls or the workflow silently unblocks.

Scope

• Push notification to workflow initiator on response received
• Notification surface: Mothership UI event + configurable webhook callback
• Payload includes: question ID, respondent, response value, timestamp
• Works for all response paths (web form, MagicLink, inbound decision Promote inbound decisions to first-class decision records #416)

Acceptance criteria

• Initiator receives a notification within seconds of response submission
• Webhook callback fires if configured
• Notification appears in Mothership event feed
• Integration test covers the full round-trip: question sent → answered → initiator notified

Depends on

#632 (web delivery provider)