0.7.0

Add customer sorting: custom order, A-Z, Z-A, most used (#1)

Closes #1. The list could only ever show insertion order.

Four modes, chosen from a control next to the search box and remembered between
launches:

- Custom order — the stored order, now rearrangeable by dragging a card.
- Name A-Z / Z-A — system locale collation, so Nordic users get æ/ø/å in the
  right place, and numeric so "Customer 2" precedes "Customer 10".
- Most used — by how often the customer's portals have been opened, breaking ties
  on most recently opened and then name so the order is stable.

Sorting is a view concern and never rewrites the stored order, so switching to
A-Z and back leaves a hand-arranged list intact. Dragging is only offered in
custom mode with no active search, since reordering a sorted or filtered list has
no meaningful result — the list says so when a search hides it.

"Most used" needs usage data, so each customer now carries openCount and
lastOpenedAt, incremented locally when a portal opens. Counted on your machine
only; nothing leaves it, and the counters survive an export/import round-trip
rather than resetting everyone's history.

One bug found while testing the drag path: the dragged id was React state, so
dragover and drop read a stale value when they fired in the same tick as
dragstart. Moved it to a ref, with the dataTransfer payload as a fallback.

18 new tests cover the sort modes, the reorder helper, locale and numeric
ordering, tie-breaking, non-mutation, and counter normalisation on import.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>