feat: add theme palettes (#1326)

Add Neutral, Indigo, Forest, and Sand palettes independently of Light, Dark, and System. Persist and hydrate the selection, add the accessible settings picker, and include the validated review fixes for keyboard navigation and Swedish copy.

messages/en.json

@@ -403,6 +403,12 @@
     "name_saved": "Name updated",
     "name_save_failed": "Could not save name",
     "section_appearance": "Appearance",
+    "palette_label": "Color palette",
+    "palette_description": "Changes accent and surface tones. Light, dark, and system continue to work independently.",
+    "palette_neutral": "Neutral",
+    "palette_indigo": "Indigo",
+    "palette_forest": "Forest",
+    "palette_sand": "Sand",
     "section_language": "Language",
     "language_description": "Choose the language for the interface. Invoices and reports always stay in Swedish.",
     "language_saved": "Language updated",

messages/sv.json

@@ -403,6 +403,12 @@
     "name_saved": "Namnet har uppdaterats",
     "name_save_failed": "Kunde inte spara namnet",
     "section_appearance": "Utseende",
+    "palette_label": "Färgpalett",
+    "palette_description": "Byter accentfärg och yttoner. Ljust, mörkt och system fortsätter fungera oberoende.",
+    "palette_neutral": "Neutral",
+    "palette_indigo": "Indigo",
+    "palette_forest": "Skog",
+    "palette_sand": "Sand",
     "section_language": "Språk",
     "language_description": "Välj språket för gränssnittet. Fakturor och rapporter förblir alltid på svenska.",
     "language_saved": "Språket har uppdaterats",