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/tsconfig.json

@@ -8,7 +8,11 @@
     "resolveJsonModule": true,
     "esModuleInterop": true,
     "baseUrl": ".",
-    "paths": { "@/*": ["src/*"] },
+    "paths": {
+      "@/*": ["src/*"],
+      "@shared/*": ["src/shared/*"],
+      "@features/*": ["src/features/*"]
+    },
     "lib": ["ES2023", "ESNext", "DOM", "DOM.Iterable"],
     "types": ["vitest/globals", "node"]
   },