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/core/context.go

@@ -10,7 +10,6 @@ import (
 	"sync"
 	"time"
 
-	"Wavelet/core/contracts"
 	"Wavelet/core/extpoints"
 )
 
@@ -237,24 +236,6 @@ func (c *Context) Setting() extpoints.SettingExtension {
 	return c.Settings()
 }
 
-// DB returns the contracts.DBService registered in the IoC container, or nil if not registered.
-func (c *Context) DB() contracts.DBService {
-	svc, err := Inject[contracts.DBService](c)
-	if err != nil {
-		return nil
-	}
-	return svc
-}
-
-// Cache returns the contracts.CacheService registered in the IoC container, or nil if not registered.
-func (c *Context) Cache() contracts.CacheService {
-	svc, err := Inject[contracts.CacheService](c)
-	if err != nil {
-		return nil
-	}
-	return svc
-}
-
 // OnDispose registers a cleanup callback function to be executed when this Context is disposed.
 // It accepts func() error, func(), or Disposer.
 func (c *Context) OnDispose(fn any) {