feat(ui): Charcoal theme, elegant selection, rounded note list, confirm sign-out

- A new Charcoal theme — neutral dark greys on the menu, note list and
  editor instead of the default's faint green cast, with matching inks;
  the green accent stays. It joins the theme picker on its own (the picker
  is data-driven from THEMES).
- The text selection is a translucent wash of the accent, not the old
  near-invisible tint and not a solid slab — visible on white and on the
  dark surfaces, keeping the text's own colour.
- The note list is a rounded card now, the same corner and border as the
  editor beside it, with a few pixels more air around the menu and the list.
- Signing out asks first: a second click within a few seconds confirms, so
  a button the pointer passes over does not drop you at the login screen.

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

web/src/lib/locales/da.js

@@ -119,6 +119,7 @@ export const da = {
 	'nav.calendar': 'Kalender',
 	'nav.settings': 'Indstillinger',
 	'nav.signOut': 'Log ud',
+	'nav.signOutConfirm': 'Tryk igen for at logge ud',
 	'nav.main': 'Hovedmenu',
 	'nav.search': 'Søg',
 	'nav.searchLong': 'Søg i opgaver og projekter',
@@ -843,6 +844,8 @@ export const da = {
 	// --- the themes -------------------------------------------------------------------
 	'theme.dark': 'Nordlys',
 	'theme.darkNote': 'Mørk med grøn accent.',
+	'theme.charcoal': 'Kul',
+	'theme.charcoalNote': 'Neutral mørkegrå.',
 	'theme.dusk': 'Skumring',
 	'theme.duskNote': 'Mørk og varm, med rav.',
 	'theme.light': 'Dagslys',