feat(lists): assign a colour to a sidebar folder

Tints the folder name and its guide line; picked from a swatch row in the folder settings.

src/ClaudeDo.Localization/locales/de.json

@@ -460,6 +460,8 @@
       "createAsFolderHint": "Ein Ordner gruppiert nur Listen in der Seitenleiste — er enthält keine Aufgaben und führt nichts aus. Listen per Drag-and-Drop hineinziehen.",
       "sectionGeneral": "ALLGEMEIN",
       "name": "Name",
+      "folderColor": "Farbe",
+      "folderColorHint": "Färbt den Ordnernamen und seine Führungslinie in der Seitenleiste.",
       "workingDirectory": "Arbeitsverzeichnis",
       "workingDirectoryPlaceholder": "(keines)",
       "browse": "Durchsuchen...",

src/ClaudeDo.Localization/locales/en.json

@@ -460,6 +460,8 @@
       "createAsFolderHint": "A folder just groups lists in the sidebar — it holds no tasks and runs nothing. Drag lists onto it to fill it.",
       "sectionGeneral": "GENERAL",
       "name": "Name",
+      "folderColor": "Colour",
+      "folderColorHint": "Tints the folder name and its guide line in the sidebar.",
       "workingDirectory": "Working directory",
       "workingDirectoryPlaceholder": "(none)",
       "browse": "Browse...",