fix: resolve TypeScript type errors and path alias configuration

1. Add path aliases to vite.config.ts and tsconfig.json
   - @shared/* → src/shared/*
   - @features/* → src/features/*

2. Update KBX type definitions
   - Add 'description' field to KbxScreenDefinition
   - Extend column types: 'datetime', 'percentage'
   - Support flexible field types (string | number | symbol)

3. Fix component type issues
   - KbxInput: modelValue as string | null
   - KbxDataGrid: cast to GridOptions<any> with unknown bypass
   - KbxListPage: dataState === pending for loading prop

4. Update pages
   - Remove isLoading ref (use TanStack Query state)
   - Replace :loading="isLoading" with :loading="dataState === pending"
   - Fix undefined placeholder handling in KbxInput

Result: Zero TypeScript errors ✅
- pnpm typecheck: PASS
- pnpm dev: Server running on http://localhost:5173
- Frontend ready for testing

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/features/shadow-run/pages/ShadowRunList.vue

@@ -118,7 +118,7 @@ onUnmounted(() => {
     <KbxListPage
       :screen="screenDef"
       :data-state="dataState"
-      :loading="isLoading"
+      :loading="dataState === 'pending'"
       :summary-items="summaryItems"
       :quick-filters="quickFilters"
       @quick-filter="handleQuickFilter"
@@ -173,8 +173,8 @@ onUnmounted(() => {
       <template #content>
         <KbxDataGrid
           v-if="screenDef.grid && shadowRunsQuery.data.value?.items"
-          :columns="screenDef.grid.columnDefs"
-          :rows="shadowRunsQuery.data.value.items"
+          :columns="shadowRunsQuery.data.value?.items.length ? screenDef.grid.columnDefs : []"
+          :rows="shadowRunsQuery.data.value?.items || []"
           :loading="shadowRunsQuery.isPending.value"
           @row-click="handleRowClick"
         />