refactor(ui) : improve styling, layout and responsive across all components

Rework CSS theme (app.css), navbar layout, dashboard page, machine detail,
catalog pages, and various form/display components for better consistency
and mobile responsiveness.

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

app/components/PageHero.vue

@@ -1,11 +1,11 @@
 <template>
   <section :class="sectionClasses">
     <div :class="contentClasses">
-      <div :class="['space-y-4', maxWidthClass]">
-        <component :is="headingTag" v-if="title" class="text-4xl font-bold">
+      <div :class="['space-y-3', maxWidthClass]">
+        <component :is="headingTag" v-if="title" class="text-4xl font-bold tracking-tight">
           {{ title }}
         </component>
-        <p v-if="subtitle" class="text-sm opacity-90">
+        <p v-if="subtitle" class="text-sm opacity-80 leading-relaxed">
           {{ subtitle }}
         </p>
         <slot />
@@ -58,9 +58,9 @@ const props = defineProps({
 })
 
 const sectionClasses = computed(() => {
-  const classes = ['hero', 'bg-gradient-to-r', props.gradientFrom, props.gradientTo, props.minHeight]
+  const classes = ['hero', 'bg-gradient-to-br', props.gradientFrom, props.gradientTo, props.minHeight]
   if (props.rounded) {
-    classes.push('rounded-lg')
+    classes.push('rounded-xl', 'overflow-hidden')
   }
   return classes
 })