docs(shared): record the Sonu+Sunny leg as its own trip

Trip 3, 2026-04-12 to 2026-04-28, 124 rows, $9,914.24. It was marked only by
tag 5 and so was invisible to every trip figure.

It reads at first like a sharing scope overlapping the group trip, because the
tag's earliest row is 17 March. It is not: that is a single advance booking
(Ticketmaster Nanterre), 8 more rows fall on the 12 April handover day and were
already held out of Europe 2026, and the remaining 115 run 13-28 April. A clean
sequential leg.

Also records that grouped payments need no schema change -- split_payments has
no unique constraint on linked_transaction_id, so one transfer can carry a row
per scope -- and that the 23 Apr Qantas booking is the flight to Bangkok
starting a solo leg, which is why it stays out of this trip.

docs/shared-expenses-design.md

@@ -203,11 +203,24 @@ fortnight of principal into spend, the error migration 0014 exists to prevent.
    marks Molina's money in all six known cases, but it is a description match on
    a free-text field. Acceptable as a *suggestion* requiring confirmation, not
    as an automatic rule.
-3. **Untracked travel, Apr–May 2026.** France ($7,020.99, 68 rows) and Singapore
+3. **Two unattributable Sonu payments.** #3 ($3,779.33, 12 Apr) and #8
-   ($2,242.05, 40 rows) between 13 April and 9 May 2026 belong to no trip. The
+   ($4,794.06, 16 May) are narrated only as "transfer", and payments are made
-   France rows begin the day after Europe 2026's end date, so this is either an
+   grouped — one transfer can cover a trip and the household tab together. That
-   extension of that trip or one or two new ones.
+   is already expressible: `split_payments` has no unique constraint on
-4. **Two unattributable Sonu payments.** #3 ($3,779.33, 12 Apr) and #8
+   `linked_transaction_id`, so one bank transfer can carry several rows, each
-   ($4,794.06, 16 May) are narrated only as "transfer". Both currently sit on
+   with its own `trip_id`. What is missing is the breakdown. Both currently sit
-   the household tab; scoping them elsewhere moves money between tabs without
+   whole on the household tab; splitting them moves money between tabs without
    changing her overall balance.
+4. **The solo leg.** A Qantas booking on 23 Apr (txn 2849, $1,366.40) is the
+   flight to Bangkok that begins a solo leg, and the Singapore spending
+   ($2,242.05, 40 rows, to 9 May) is solo — not shared. It has no trip record.
+   Worth one if trip *cost* is wanted for it; nothing about sharing depends on
+   it.
+
+## Resolved
+
+- **Europe — Sonu + Sunny** (trip 3, 2026-04-12 → 2026-04-28, 124 rows,
+  $9,914.24). The leg after the group trip, previously marked only by tag 5 and
+  invisible to trip analytics. Includes one advance booking on 17 Mar
+  (Ticketmaster Nanterre) and the 12 Apr handover-day rows, which were already
+  held out of Europe 2026.