feat: add UTM parameter data to insights bookings CSV download

[CarinaWolli]

What does this PR do?

Adds UTM parameter data (utm_source, utm_medium, utm_campaign, utm_term, utm_content) to the CSV download from /insights bookings, matching the format already used in the /insights/routing CSV download.

Previously, the bookings CSV export did not include any UTM tracking data. UTM data is stored on the Tracking model (one-to-one relation with Booking via @@unique([bookingId])). The routing form responses CSV already includes UTM columns (see routing-events.ts lines 191-195), so this change brings parity.

Changes:

• Extended the BookingWithAttendees type to include the tracking relation (nullable, since not all bookings have tracking data)
• Added the tracking relation with UTM fields to the Prisma select in getCsvData
• Added getUtmDataForBooking helper to extract UTM data via booking.tracking, with empty-string defaults for null values (matching routing CSV behavior)
• UTM columns appear at the end of each CSV row
• Added unit tests for getUtmDataForBooking and UTM inclusion in transformBookingsForCsv, updated existing test fixtures and snapshots

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

1. Create bookings that have UTM parameters (book via a URL with ?utm_source=test&utm_medium=email etc.)
2. Go to /insights, select a date range covering those bookings
3. Click Download → As CSV
4. Open the CSV and confirm utm_source, utm_medium, utm_campaign, utm_term, utm_content columns are present with correct values
5. Compare with the routing CSV download from /insights/routing to verify the format matches

Human Review Checklist

• Verify the tracking relation JOIN in getCsvData doesn't significantly impact query performance for large exports
• Confirm empty-string default for missing UTM values (matching routing CSV) vs. null is the desired behavior
• Check that the additional bookingsByUid Map construction in transformBookingsForCsv is acceptable (iterates bookings array once more per batch of up to 100)

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Link to Devin run: https://app.devin.ai/sessions/9683a4a30f3344f7a52a2954eb9119e7
Requested by: @CarinaWolli

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[cubic-dev-ai]

No issues found across 2 files

[eunjae-lee]

the code change looks good !