feat: add Danish locale

TRANSLATION_DA_NOTES.md

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+# Danish translation notes
+
+No blocking translation issues found.
+
+A few terms involved product-style judgment calls:
+
+- `notes.title` / `nav.notes` → **"Tavle"** to match the family-planner/board feel better than a literal "Noter".
+- `housekeeping.title` → **"Rengøringsområde"** while navigation keeps **"Rengøring"** for shorter UI labels.
+- `dashboard.title` / `nav.dashboard` → **"Oversigt"** to stay natural in Danish UI copy.
+- Existing non-English source strings inside `en.json` (mainly a few German settings labels) were translated into Danish from their apparent UI meaning.
+
+Verified:
+
+- `public/locales/da.json` parses as valid JSON.
+- `da.json` matches `en.json` key structure exactly.
+- Placeholder tokens such as `{{name}}`, `{{count}}`, `{{date}}`, and `{{title}}` were preserved exactly.