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/colors.js

@@ -21,17 +21,20 @@
  * carries a `--color-<id>` token for each, and a Go test reads this file to check
  * the server's list of accepted names has not drifted from it.
  */
+// `name` is a key rather than a word: the picker calls `t()` on it. The ids stay
+// exactly as they are — they are what the database stores, and `internal/store`
+// has a test that reads them out of this file.
 export const COLORS = [
-	{ id: 'graphite', name: 'Grafit' },
-	{ id: 'tomato', name: 'Tomat' },
-	{ id: 'amber', name: 'Rav' },
-	{ id: 'lime', name: 'Lime' },
-	{ id: 'green', name: 'Grøn' },
-	{ id: 'teal', name: 'Petrol' },
-	{ id: 'blue', name: 'Blå' },
-	{ id: 'indigo', name: 'Indigo' },
-	{ id: 'violet', name: 'Violet' },
-	{ id: 'magenta', name: 'Magenta' }
+	{ id: 'graphite', name: 'color.graphite' },
+	{ id: 'tomato', name: 'color.tomato' },
+	{ id: 'amber', name: 'color.amber' },
+	{ id: 'lime', name: 'color.lime' },
+	{ id: 'green', name: 'color.green' },
+	{ id: 'teal', name: 'color.teal' },
+	{ id: 'blue', name: 'color.blue' },
+	{ id: 'indigo', name: 'color.indigo' },
+	{ id: 'violet', name: 'color.violet' },
+	{ id: 'magenta', name: 'color.magenta' }
 ];
 
 /** The CSS variable a colour id paints with, falling back to the default. */