feat: add build version display to all views

Add build version indicator to verify code updates:

1. Create BuildVersion.vue component:
   - Displays in top-right corner (fixed position)
   - Format: YYYYMMDDHHMMSS-gitHash
   - Example: 20260725133504-39ce37e

2. Update vite.config.ts:
   - Inject __BUILD_VERSION__ global variable
   - Generated from build time + git commit hash

3. Add to App.vue:
   - Shown on all views automatically
   - Z-index: 9999 (always visible)

4. Add vite-env.d.ts:
   - TypeScript declarations for __BUILD_VERSION__

Purpose:
- User can verify if browser loaded latest code
- Easy to confirm updates are deployed
- No need to check source code

Location: Top-right corner, fixed position
Format: Monospace font, small text, subtle styling

src/vite-env.d.ts

@@ -0,0 +1,11 @@
+/// <reference types="vite/client" />
+
+declare const __BUILD_VERSION__: string
+
+interface ImportMetaEnv {
+  readonly VITE_APP_TITLE: string
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv
+}