Runsignup connector: field_mappings plumbing for question → Effort routing

[moveson]

Refs #1998. This is the plumbing PR — UI for race-director-side configuration is follow-up.

What it does

Adds a per-event-Connection JSON column (field_mappings) that the Runsignup sync pipeline reads and applies, routing question responses into the Effort model's comments / emergency_contact / emergency_phone columns.

Mapping shape

Stored on connections.field_mappings (jsonb, defaults to []):

[
  { "source_question_id": 100, "destination": "emergency_contact" },
  { "source_question_id": 200, "destination": "comments", "suppress_when": "No", "value_when_present": "First Attempt" },
  { "source_question_id": 201, "destination": "comments" }
]

• destination: one of comments, emergency_contact, emergency_phone.
• suppress_when: skip this mapping when the response exactly matches this string.
• value_when_present: use this string instead of the raw response (mostly relevant for comments — e.g. emit "First Attempt" rather than the literal "Yes").
• Multiple comments-mapped questions concatenate in mapping order via ", ".

Layers changed

Layer	Change
Migration	add_column :connections, :field_mappings, :jsonb, default: [], null: false
Connectors::Runsignup::Request::GetParticipants	passes include_questions=T so question_responses come back from AWS
Connectors::Runsignup::Models::Participant	adds :comments, :emergency_contact, :emergency_phone slots
Connectors::Runsignup::FetchEventParticipants	accepts field_mappings: kwarg, applies it via new attributes_from_field_mappings helper
Interactors::SyncRunsignupParticipants	reads field_mappings off each per-event runsignup Connection, forwards it; new attrs added to RELEVANT_ATTRIBUTES

Configuring a race manually (until UI lands)

conn = event.connections.from_service(:runsignup).find_by(source_type: "Event")
conn.update!(field_mappings: [
  { "source_question_id" => 74423,  "destination" => "emergency_contact" },
  { "source_question_id" => 74424,  "destination" => "emergency_phone" },
  { "source_question_id" => 182149, "destination" => "comments", "suppress_when" => "No", "value_when_present" => "First Attempt" },
  { "source_question_id" => 182151, "destination" => "comments" },
  { "source_question_id" => 182153, "destination" => "comments" },
])

Next sync from the connection management page will populate effort.comments, effort.emergency_contact, effort.emergency_phone for that event's participants.

Out of scope (follow-up PR)

• UI on the connection setup page for picking question_id → destination via a dropdown.
• Auto-detection / "suggest a mapping" assistance.

Test plan

• spec/lib/connectors/runsignup/fetch_event_participants_spec.rb — 5 new examples covering mapping application, suppress rule, value_when_present override, no-mappings fallback, missing question_responses payload.
• spec/services/interactors/sync_runsignup_participants_spec.rb — 2 new examples covering field_mappings flow-through and the resulting Effort column writes.
• Rubocop clean on touched files.
• Manual end-to-end against race 174571 once this is merged: configure mapping via console, trigger sync from UI, verify Effort comments/emergency columns populated.

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