feat: v2 Vue3 frontend + multiple optimizations

- New Vue 3 + Vite frontend at /v2/ (OLED dark theme, Fira Sans/Code)
- Date selector: support day/week/month range (backend unchanged)
- SSE auto-reconnect (up to 3 retries)
- Visibility polling pause (dashboard pauses when tab hidden)
- Friendly Chinese HTTP error messages
- Cancel task with confirmation in Dashboard
- Split AiWorkflowService (1700->845 lines):
  - AiApiService: AI API calls + streaming
  - ExcelExportService: POI Excel generation
- Dockerfile: 3-stage build (Node frontend -> Maven -> JRE)
- WebApplication.java: System.out -> Logger
- .gitignore: v2 build output, backup dirs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Makefile

@@ -1,3 +1,10 @@
+# ============================================================
+# Docker Hub 镜像代理（默认使用 docker.1ms.run 加速）
+# 如果需要切换回 Docker Hub：
+#   DOCKER_REGISTRY_MIRROR=docker.io/library make up
+# ============================================================
+DOCKER_REGISTRY_MIRROR ?= docker.1ms.run/library
+
 .PHONY: up down status
 
 COMPOSE_CMD := $(shell if command -v docker >/dev/null 2>&1 && docker compose version >/dev/null 2>&1; then echo "docker compose"; elif command -v docker-compose >/dev/null 2>&1; then echo "docker-compose"; fi)
@@ -5,7 +12,7 @@ BUILD_ENV := DOCKER_BUILDKIT=1 COMPOSE_DOCKER_CLI_BUILD=1
 
 up:
 	@if [ -z "$(COMPOSE_CMD)" ]; then echo "docker compose/docker-compose not found"; exit 1; fi
-	@$(BUILD_ENV) $(COMPOSE_CMD) up -d --build
+	@REGISTRY_MIRROR=$(DOCKER_REGISTRY_MIRROR) $(BUILD_ENV) $(COMPOSE_CMD) up -d --build
 	@echo "Application is starting at http://localhost:18088"
 
 down: