feat: finalist.editAttendees with cutoff and diff-based update

Team-lead-only mutation that replaces the AttendingMember roster on a
CONFIRMED finalist confirmation. Diffs the requested user list against
existing rows: kept rows are updated in place (preserving FlightDetail),
removed rows are deleted, added rows are created. Enforces:
  - team-lead role
  - CONFIRMED status
  - defaultAttendeeCap
  - team-membership of every supplied userId
  - cutoff = LIVE_FINAL.windowOpenAt − attendeeEditCutoffHours (default 48)

Audit-logged as FINALIST_EDIT_ATTENDEES with the diff payload.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/helpers.ts

@@ -53,7 +53,7 @@ export async function createTestUser(
 // ─── Program Factory ───────────────────────────────────────────────────────
 
 export async function createTestProgram(
-  overrides: Partial<{ name: string; year: number }> = {},
+  overrides: Partial<{ name: string; year: number; defaultAttendeeCap: number }> = {},
 ) {
   const id = uid('prog')
   return prisma.program.create({
@@ -62,6 +62,9 @@ export async function createTestProgram(
       name: overrides.name ?? `Test Program ${id}`,
       year: overrides.year ?? 2026,
       status: 'ACTIVE',
+      ...(overrides.defaultAttendeeCap !== undefined
+        ? { defaultAttendeeCap: overrides.defaultAttendeeCap }
+        : {}),
     },
   })
 }