Add Mermaid data-flow diagram to README

Author: DiogoRibeiro7

README.md

@@ -22,17 +22,20 @@ The three packages share contract identifiers (`source_id`, `document_id`, `chun
 
 Data flow:
 
-```text
-sources ──▶ knowledge_ingestion ──▶ documents.jsonl, chunks.jsonl, lineage.jsonl
-                                          │
-                                          ▼
-runtime ──▶ observability_analytics ──▶ interactions.jsonl, retrieval_traces.jsonl
-                                          │
-                                          ▼
-                                   dataset_foundry ──▶ prompt_response.jsonl,
-                                                       retrieval_evaluation.jsonl,
-                                                       split_assignments.jsonl,
-                                                       dataset_manifest.json
+```mermaid
+flowchart TD
+    sources([source documents]) --> KI[knowledge_ingestion]
+    runtime([runtime LLM traces]) --> OA[observability_analytics]
+
+    KI --> docs[documents.jsonl<br/>chunks.jsonl<br/>lineage.jsonl]
+    OA --> traces[interactions.jsonl<br/>retrieval_traces.jsonl]
+
+    docs --> DF[dataset_foundry]
+    traces --> DF
+    DF --> out[prompt_response.jsonl<br/>retrieval_evaluation.jsonl<br/>split_assignments.jsonl<br/>dataset_manifest.json]
+
+    classDef pkg fill:#2a6db2,stroke:#1b4a7a,color:#fff;
+    class KI,OA,DF pkg;
 ```
 
 See [docs/architecture.md](docs/architecture.md) for boundaries and [docs/integration.md](docs/integration.md) for the full handoff contract.