D-02: support multiple vaccinators in availability flow

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What changed

Added a dedicated vaccinators step to the availability add and edit journeys.

The flow now captures whether a session has more than one vaccinator on its own screen, using radios with a conditional reveal for the vaccinator count. The vaccinator count is persisted on availability records, shown on check answers and the availability list, and seeded for Riverside Pharmacy weekday availability.

Why it changed

Round 1 research showed that larger vaccination sites may run a single session with multiple vaccinators, and that the prototype should support both single-vaccinator and multi-vaccinator setup paths.

Traceability

• Assumption: A-05 availability is managed per vaccinator; A-15 one vaccinator per session matches mental model
• Finding: Round 1, finding 2
• Decision: D-02 support multiple vaccinators within a session setup
• Issue: D-02: Support multiple vaccinators within a session setup #6

Validation

• Checked edited routes, templates, and seed files for workspace errors
• Reproduced and fixed the runtime error on /sites/site_2/availability/avail_3/edit/vaccinators
• Verified the vaccinator edit route renders successfully with a valid session

Remaining uncertainty

This change captures and surfaces multi-vaccinator sessions, but it does not yet remodel booking-slot concurrency so one session can represent parallel bookings at the same time.

What to test next

Test whether users understand the separate vaccinators step, the conditional reveal for count, and the new vaccinator summary information in add and edit flows. Also test whether larger-site users expect multi-vaccinator sessions to affect booking capacity directly.

Closes #6