feat(ai-sdk): legal-corpus structure endpoint + coverage page

Expose GET /sdk/v1/rag/legal-corpus, which scrolls the eur-lex legal
corpus (filtered to a few hundred points regardless of total size) and
aggregates each ingested act's composition: distinct articles, annexes,
recitals and chunk count. Surface it as a new section on /sdk/coverage so
the ingested corpus is no longer a black box — a developer SEES what each
act actually contains, not only its name.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ai-compliance-sdk/internal/app/routes.go

@@ -161,6 +161,7 @@ func registerRAGRoutes(v1 *gin.RouterGroup, h *handlers.RAGHandlers) {
 		ragRoutes.GET("/corpus-status", h.CorpusStatus)
 		ragRoutes.GET("/corpus-versions/:collection", h.CorpusVersionHistory)
 		ragRoutes.GET("/scroll", h.HandleScrollChunks)
+		ragRoutes.GET("/legal-corpus", h.LegalCorpusStructure)
 	}
 }