Auto-emit work-trip parking to your employer's expense report

When you drive a business trip, parking is annoying to track manually. With expense routing on, Turtini does it for you.

**The condition**
A session auto-emits an expense line ONLY when all four are true:
1. The plate is on file with your account.
2. The plate has a `defaultExpenseOrgId` set (the employer you want billed).
3. The session overlaps a trip on `/me/trips` with `tripType: 'work'`.
4. The session was paid (either auto-charged to your card or comped).

If any of the four fail, no line is written. (Personal sessions charge your card and stay on /me/parking; that's it.)

**What gets written**
The auto-pay function calls into your employer's Expense Reports module:
• Finds your open monthly report for the period (e.g. "June 2026"). If you don't have one, a draft is created.
• Appends an `expenseItems` line: category `transportation`, description `Parking — <lot name> (<plate>)`, amount = the session total.
• Updates the report's running `totalAmount`.
• Stamps the session with `expenseItemId` + `expenseReportId` so the same session can never be double-billed.

**What your finance team sees**
A normal line on the normal report. Your manager approves the report as usual; reimbursement (if your employer pays you back directly) or pass-through (if Turtini charged the employer's account) follows your existing flow.

**Editing a wrong line**
The expense item is owned by your employer's report — they can edit description, recategorize, or delete it. If they delete the line, the session keeps `expenseEmittedAt` set so the auto-emit won't re-fire on a later session-write. To force a re-emit, an admin can clear `expenseItemId` on the session document.

**Multiple plates, multiple employers**
Each plate has its own `defaultExpenseOrgId`. Drive the company car to your employer's site → routes there. Drive your personal car on a personal trip → no routing. Switch between two consulting clients by switching the plate's expense org via /me/parking → Plates.