feat(offline): ride out short connection drops instead of losing the save

A save made while the connection blips for a few seconds is retried rather
than reverted: the request layer keeps trying a network failure for a
fifteen-second window, waking the instant the OS reports a link again, and
only falls back to the existing error path if the drop outlasts it. A quiet
"reconnecting" pill appears if the wait passes about a second, and leaves
the moment it heals — so a two-second blip is felt as nothing at all.

This is deliberately not offline mode: the app is a live view of a shared
list, so there is no cache to work in with no server and no write log to
reconcile. It is only the blip, ridden out. A server error (4xx/5xx) is the
server answering and is not retried; an aborted request (a superseded
search) is left to propagate.

Kristian: an offline function for when the net drops for short periods,
seconds. Shared items stay server-authoritative — nothing is edited against
a stale copy for longer than the blip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/lib/locales/da.js

@@ -130,6 +130,8 @@ export const da = {
 	'nav.toggleTheme': 'Skift mellem lyst og mørkt tema',
 	'nav.offline': 'Offline',
 	'nav.offlineHint': 'Ændringer fra andre vises ikke lige nu',
+	'net.reconnecting': 'Genopretter forbindelse…',
+	'net.offline': 'Ingen forbindelse',
 	'nav.doItToday': 'Gør det i dag',
 
 	// --- the sidebar's own sections ------------------------------------------------