feat: UI polish, lint fixes, onboarding redesign, help page expansion, and test improvements

Broad update across dashboard pages, components, extensions, and lib code. Includes ESLint config additions, onboarding flow redesign, settings page refactor, help page content expansion, dead code removal, and test mock fixes. Adds dev docs and public assets.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

components/onboarding/Step1EntityType.tsx

@@ -45,15 +45,8 @@ export default function Step1EntityType({ initialData, onNext, isSaving }: Step1
   }
 
   return (
-    <div className="space-y-6">
-      <div className="text-center">
-        <h1 className="text-3xl font-bold tracking-tight">Välkommen!</h1>
-        <p className="text-muted-foreground mt-2">
-          Låt oss börja med att ställa in din verksamhet. Vilken företagsform har du?
-        </p>
-      </div>
-
-      <div className="grid gap-3 max-w-lg mx-auto">
+    <div className="space-y-8">
+      <div className="grid gap-3">
         {entityOptions.map((option) => {
           const Icon = option.icon
           const isSelected = selected === option.value