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/lib/components/BoardView.svelte

@@ -13,6 +13,7 @@
 	import { TASK, startDrag, carries, accept } from '$lib/dnd.js';
 	import { focusOnMount } from '$lib/focus.js';
 	import TaskRow from './TaskRow.svelte';
+	import { t } from '$lib/i18n.svelte.js';
 
 	let { project, sections, canEdit, onsectionadded } = $props();
 
@@ -143,7 +144,7 @@
 				{/each}
 
 				{#if !tasks.length}
-					<p class="empty">Tom</p>
+					<p class="empty">{t('view.emptySection')}</p>
 				{/if}
 			</div>
 		</section>
@@ -156,8 +157,8 @@
 					<input
 						bind:value={name}
 						use:focusOnMount
-						placeholder="Sektionens navn"
-						aria-label="Ny sektion"
+						placeholder={t('view.sectionName')}
+						aria-label={t('view.newSection')}
 						onblur={() => !name.trim() && (adding = false)}
 						onkeydown={(e) => e.key === 'Escape' && (adding = false)}
 					/>
@@ -168,7 +169,7 @@
 					onclick={() => {
 						adding = true;
 						name = '';
-					}}>+ Tilføj sektion</button
+					}}>{t('view.addSection')}</button
 				>
 			{/if}
 		</section>