feat: add mobile responsiveness support

- Hamburger menu + drawer sidebar for mobile navigation
- Auto-collapse chat session list on mobile
- Responsive grids, modals, forms, and settings
- Touch-friendly nav items (44px targets)
- Skills page sidebar toggle on mobile
- Memory sections stack vertically on mobile

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

src/components/jobs/JobFormModal.vue

@@ -112,7 +112,7 @@ function handleClose() {
     v-model:show="showModal"
     preset="card"
     :title="isEdit ? t('jobs.editJob') : t('jobs.createJob')"
-    :style="{ width: '520px' }"
+    :style="{ width: 'min(520px, calc(100vw - 32px))' }"
     :mask-closable="!loading"
     @after-leave="emit('close')"
   >