chore(frontend): engineering baseline per guide ch.8

- toolchain: vitest+jsdom (15 tests green: permission pure functions
  exhaustive, storage migration), prettier (printWidth 120 to fit the
  dense existing style + 700-line page budget), commitlint conventional
- npm scripts: typecheck / format / test / lint:fix; build fingerprint
  __APP_VERSION__ (version+git hash+build time) shown in Settings > about
- git hooks via core.hooksPath=frontend/.husky: pre-commit lint-staged
  (prettier + eslint --fix best-effort), commit-msg commitlint
- permission pure functions extracted to lib/permissions.ts (single
  source consumed by useAuth/useLogin); AuditLogsPage filters on URL
- backend: resp package unit tests; health version constant aligned
  with frontend package.json

backend/cmd/server/main.go

@@ -14,6 +14,9 @@ import (
 	"gorm.io/gorm"
 )
 
+// AppVersion 与前端 package.json 版本保持同步
+const AppVersion = "0.4.0"
+
 func main() {
 	// Load config
 	config.Init()
@@ -73,7 +76,7 @@ func main() {
 
 	// Health check
 	r.GET("/health", func(c *gin.Context) {
-		c.JSON(200, gin.H{"status": "ok", "version": "0.3.1", "backend": "go"})
+		c.JSON(200, gin.H{"status": "ok", "version": AppVersion, "backend": "go"})
 	})
 
 	// Routes