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/downstream/plugins/custom_example/plugin.go

@@ -8,9 +8,10 @@ package custom_example
 import (
 	"net/http"
 
+	"github.com/gin-gonic/gin"
+
 	"Wavelet/core"
 	"Wavelet/core/contracts"
-	"github.com/gin-gonic/gin"
 )
 
 // Plugin implements core.Plugin for the custom_example downstream plugin.