feat(i18n): the interface speaks both languages

The account has had a `locale` since the beginning and it only chose which grammar
quick add read a line with — so picking English changed nothing anybody could see,
and the field said so honestly: "Sprog i hurtig tilføjelse". It says "Sprog" now,
because it means it.

Every component goes through `t()`. Danish is the source: a key missing from
English falls through to Danish rather than to the key, because a Danish sentence
in an English screen can be read and `settings.notifications.title` cannot.

`tag()` is the single place `Intl` is asked. Before, `'da-DK'` was written into a
dozen components, and that is the half of a translation that gets left behind — an
English interface still saying "24. aug." is exactly the shape of a job half done.
There is a smoke test that switches to English and refuses to see a Danish month
name in the calendar's heading.

Colour and theme names are keys now. `colors.js` keeps its ids untouched — they
are what the database stores, and `internal/store` reads them out of that file —
but `name` is `'color.tomato'`, resolved where it is drawn.

The Inbox keeps its name. It is a project row the server creates at signup, not a
string in the interface, and it can be renamed like any other project.

Four copies of "3 hours ago" became one, in `web/src/lib/when.js`. They had
already drifted: one said "aldrig logget ind", another "aldrig", and two stopped
at days where the others carried on to a date.

Routes stay Danish. `/indstillinger`, `/projekt`, `/uddelegeret` are bookmarks and
they are in every smoke test; translating them buys nothing and costs both.

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

web/src/routes/upcoming/+page.svelte

@@ -20,6 +20,7 @@
 	import TaskRow from '$lib/components/TaskRow.svelte';
 	import QuickAdd from '$lib/components/QuickAdd.svelte';
 	import CalendarView from '$lib/components/CalendarView.svelte';
+	import { t } from '$lib/i18n.svelte.js';
 
 	let days = $state([]);
 
@@ -80,9 +81,9 @@
 
 <div class="view" class:wide={upcomingView.mode !== 'list'}>
 	<header>
-		<h1>Kommende</h1>
-		<div class="views" role="group" aria-label="Visning">
-			{#each [['list', 'Liste'], ['week', 'Uge'], ['calendar', 'Måned']] as [value, label]}
+		<h1>{t('view.upcoming')}</h1>
+		<div class="views" role="group" aria-label={t('view.mode')}>
+			{#each [['list', t('view.list')], ['week', t('view.week')], ['calendar', t('view.month')]] as [value, label]}
 				<button
 					class:active={upcomingView.mode === value}
 					onclick={() => upcomingView.set(value)}