refactor(core): align with cordis spatiotemporal composability architecture

- Purify core micro-kernel by removing context hardcoded helpers and reverse dependencies
- Eliminate init() side effects in infra plugins with reversible lifecycle disposal
- Completely isolate plugins by removing cross-plugin imports and using core/contracts
- Introduce TaskService and RiskControlService contracts for unified cross-plugin APIs
- Regenerate Swagger documentation and update developer guide matrix
- Achieve 0 violations in check_cordis_architecture.sh and 100% test pass

backend/pkg/cache/disk/cache.go

@@ -88,6 +88,20 @@ func New(basePath string) *Cache {
 	return c
 }
 
+var (
+	defaultCache     *Cache
+	defaultCacheOnce sync.Once
+)
+
+// Default returns the default global disk cache instance.
+func Default() *Cache {
+	defaultCacheOnce.Do(func() {
+		defaultCache = New("uploads/diskcache")
+		go defaultCache.StartCleanupWorker(10 * time.Minute)
+	})
+	return defaultCache
+}
+
 // Set stores a key-value pair in the cache.
 // Use DefaultExpiration for the configured default TTL, NoExpiration for no
 // TTL, or a positive duration for a business-specific TTL.

backend/pkg/idgen/snowflake.go

@@ -8,8 +8,9 @@ import (
 	"fmt"
 	"log"
 
-	"Wavelet/pkg/config"
 	"github.com/bwmarrin/snowflake"
+
+	"Wavelet/pkg/config"
 )
 
 // 2025-12-01 00:00:00 UTC 的毫秒时间戳

backend/pkg/testhelper/gin.go

@@ -4,8 +4,9 @@
 package testhelper
 
 import (
-	"Wavelet/pkg/response"
 	"github.com/gin-gonic/gin"
+
+	"Wavelet/pkg/response"
 )
 
 // NewTestGinEngine 创建带 ErrorHandlerMiddleware 的 Gin 引擎，与生产环境错误响应行为一致。

backend/pkg/testhelper/test_helper.go

@@ -9,13 +9,14 @@ import (
 	"testing"
 	"time"
 
-	cachepkg "Wavelet/plugins/infra/cache"
-	db "Wavelet/plugins/infra/database"
 	"github.com/alicebob/miniredis/v2"
 	"github.com/glebarez/sqlite"
 	"github.com/redis/go-redis/v9"
 	"github.com/redis/go-redis/v9/maintnotifications"
 	"gorm.io/gorm"
+
+	cachepkg "Wavelet/plugins/infra/cache"
+	db "Wavelet/plugins/infra/database"
 )
 
 // SystemConfig 测试用系统配置表