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/genveje/+page.svelte

@@ -1,32 +1,36 @@
 <script>
 	/** The shortcuts, listed. Mapped to Todoist's so muscle memory carries over. */
-	const groups = [
+	import { t } from '$lib/i18n.svelte.js';
+
+	const groups = $derived([
 		{
-			title: 'Navigation',
+			title: t('keys.navigation'),
 			keys: [
-				['q', 'Hop til feltet “tilføj opgave”'],
-				['t', 'I dag'],
-				['u', 'Kommende'],
-				['⌘K / Ctrl+K', 'Søg'],
-				['?', 'Denne side']
+				['q', t('keys.jumpToQuickAdd')],
+				['t', t('nav.today')],
+				['u', t('nav.upcoming')],
+				['⌘K / Ctrl+K', t('nav.search')],
+				['?', t('keys.thisPage')]
 			]
 		},
 		{
-			title: 'I quick add',
+			title: t('keys.inQuickAdd'),
 			keys: [
-				['#projekt', 'Læg opgaven i et projekt'],
-				['@etiket', 'Sæt en etiket'],
-				['p1 – p4', 'Prioritet'],
-				['i morgen, på fredag, om 3 dage', 'Dato — dansk og engelsk'],
-				['kl 10, 14:30, 7pm', 'Klokkeslæt'],
-				['Esc', 'Ryd feltet']
+				['#projekt', t('keys.intoProject')],
+				['@etiket', t('keys.setLabel')],
+				['p1 – p4', t('keys.priority')],
+				// The examples stay in both languages, because the parser takes both
+				// and the point of the line is what you can actually type.
+				['i morgen, på fredag, om 3 dage', t('keys.date')],
+				['kl 10, 14:30, 7pm', t('keys.time')],
+				['Esc', t('keys.clear')]
 			]
 		}
-	];
+	]);
 </script>
 
 <div class="view">
-	<h1>Genveje</h1>
+	<h1>{t('keys.title')}</h1>
 	{#each groups as group}
 		<section>
 			<h2>{group.title}</h2>