Select contacts, and empty an address book

Raised on #174 as the other half of a migration -- import, notice
something is wrong, empty the book, correct the export, import again --
and tracked as #277.

The gap turned out to be wider than the ask. Contacts had no multi-select
at all: the only delete in the module was the cross on a single card's
pane, one card and one confirmation at a time. `destroyCards` has taken a
list and batched it against maxObjectsInSet since #218, and nothing in
the UI ever handed it more than one id. So "empty this address book" was
missing, and so was "delete these fourteen".

The list now has checkboxes, on hover the way the message list's are, and
always on a touchscreen where there is no hover to reveal them.
Shift-click takes the run between two rows. The search box gives way to a
selection bar rather than sitting beside it, because what the count
promises is what the search left on screen. A selection is cleared when
the book being shown changes, since carrying it across would leave a
count describing rows that are no longer there and a Delete aimed at
them.

Emptying a book is in the book's own menu, beside the import and export
that moved there in #226, and separate from Delete, which takes the book
with it. A default book cannot be deleted and can perfectly well be
emptied, which is most of the reason it is its own entry.

The part that is not a deletion, and the reason this is not one destroy
over everything in the book: a card filed in two books belongs to both,
and `ContactCard/set destroy` takes it away from both at once. Emptying
one book must not empty another, so a card with a second home is patched
out of this one and left alone. That is reported separately afterwards,
because it would otherwise look like contacts that refused to go.

`destroyCards` now answers with what the server confirmed rather than
throwing on the first refusal. A refusal that took half a selection with
it still deleted the other half, and an error saying only that it failed
sends somebody looking for contacts that are already gone. Both callers
report the count and the reason apart.

Emptying a shared book is deliberately not offered: the cards live in the
owner's account and this client has no path to write there.

One bug found by driving the built app rather than by any test, and worth
recording because of where it hid. The range a shift-click covers was
measured inside the `setPicked` updater -- which React runs when it gets
round to rendering, by which time the anchor ref has already been moved
to the row that *ended* the range. Every shift-click selected exactly one
row, and every store assertion still passed, because nothing was wrong
below the component. The anchor is read before the updater now, and the
contacts view has its first component tests: ten of them, six of which
fail if the measurement moves back inside.

Twelve new strings, in all nine catalogues, so nothing new falls back to
English.

web/src/locales/es.ts

@@ -1295,6 +1295,15 @@ export const catalog: Catalog = {
     // Sentences that lib/ and store/ were building in English, and the two
     // swipe labels that reach t() through a variable and so were invisible
     // to a scan for t("literal"). See #259.
+    // ── Emptying an address book, and deleting a selection (#277) ──
+    "This cannot be undone.": "Esto no se puede deshacer.",
+    "Some could not be deleted: {error}": "Algunos no se pudieron eliminar: {error}",
+    "It was not deleted": "No se ha eliminado",
+    "Empty address book": "Vaciar esta libreta de direcciones",
+    "There is nothing in it to delete": "No hay nada dentro que eliminar",
+    "Empty “{name}”?": "¿Vaciar «{name}»?",
+    "Delete them": "Eliminarlos",
+    "Nothing was deleted": "No se ha eliminado nada",
   },
   plurals: {
     // ── Third pass ─────────────────────────────────────────────────────
@@ -1346,5 +1355,10 @@ export const catalog: Catalog = {
     "Marked {n} messages as read": { one: "{n} mensaje marcado como leído", other: "{n} mensajes marcados como leídos" },
     "in {n} folders": { one: "en {n} carpeta", other: "en {n} carpetas" },
     "Deleted {n} messages": { one: "{n} mensaje eliminado", other: "{n} mensajes eliminados" },
+    // ── Emptying an address book, and deleting a selection (#277) ──
+    "Delete {n} contacts?": { one: "¿Eliminar {n} contacto?", other: "¿Eliminar {n} contactos?" },
+    "Deleted {n} contacts": { one: "Se ha eliminado {n} contacto", other: "Se han eliminado {n} contactos" },
+    "{n} contacts will be deleted. This cannot be undone.": { one: "Se eliminará {n} contacto. Esto no se puede deshacer.", other: "Se eliminarán {n} contactos. Esto no se puede deshacer." },
+    "{n} were also in other address books and were only removed from this one": { one: "{n} contacto también estaba en otra libreta de direcciones y solo se ha quitado de esta", other: "{n} contactos también estaban en otras libretas de direcciones y solo se han quitado de esta" },
   },
 };