migrate dashboard to real HeroUI v3 components and neutral theme

The frontend was built against HeroUI v2 props/classes (variant="light"/"flat",
color="primary", startContent, text-tiny, <Avatar src=/name=>) while
@heroui/react ^3.2.1 is installed, so most styling was silently ignored.
Rewrites every page/component onto the actual v3 API (variant/color enums,
Tooltip/Dropdown trigger-content structure, Avatar.Image/Fallback via a new
AppAvatar helper) and replaces the custom orange branding with HeroUI's
neutral default theme tokens. Also compacts the dashboard stat tiles, narrows
the sidebar, and swaps the activity stat grid for a single-hue comparison bar
chart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/shared/LoadingSkeleton.tsx

@@ -1,4 +1,4 @@
-import { Card, CardContent } from '@heroui/react';
+import { Card, CardContent, Skeleton } from '@heroui/react';
 
 type Props = {
   lines?: number;
@@ -8,10 +8,10 @@ export function LoadingSkeleton({ lines = 3 }: Props) {
   return (
     <div className="flex flex-col gap-3">
       {Array.from({ length: lines }).map((_, i) => (
-        <Card key={i} className="animate-pulse border border-default-100 bg-default-50/30">
-          <CardContent className="p-5">
-            <div className="h-4 w-3/4 rounded-lg bg-default-200/50" />
-            {i < 2 && <div className="mt-3 h-3 w-1/2 rounded-lg bg-default-200/30" />}
+        <Card key={i}>
+          <CardContent className="gap-2 p-5">
+            <Skeleton className="h-4 w-3/4 rounded-lg" />
+            {i < 2 && <Skeleton className="mt-3 h-3 w-1/2 rounded-lg" />}
           </CardContent>
         </Card>
       ))}