docs: add architecture and veins documentation

- System overview, artery hierarchy, build flow, room config diagrams
- Veins docs: Jira, Slack, Google OAuth
- Shunts docs: MercadoPago mock
- DOT source files with generated SVGs
- HTML viewers with navigation and full-screen mode

Solves:
- Freelance work standardization
- Missing infrastructure replication (shunts)
- Reliable testing environment (BDD -> Gherkin -> Tests)

docs/veins/mercadopago-shunt.dot

@@ -0,0 +1,64 @@
+digraph MercadoPagoShunt {
+    rankdir=LR;
+    compound=true;
+    fontname="Helvetica";
+    node [fontname="Helvetica", fontsize=11, shape=box, style="rounded,filled"];
+    edge [fontname="Helvetica", fontsize=10];
+
+    labelloc="t";
+    label="MercadoPago Shunt - Mock Payment Flow";
+    fontsize=16;
+
+    // Client App
+    subgraph cluster_client {
+        label="Managed Room (e.g., AMAR)";
+        style=filled;
+        color="#E8F5E9";
+        fillcolor="#E8F5E9";
+
+        backend [label="Backend\n(Django/FastAPI)", fillcolor="#C8E6C9"];
+    }
+
+    // Shunt
+    subgraph cluster_shunt {
+        label="Shunt (artery/shunts/mercadopago)";
+        style=filled;
+        color="#FFF3E0";
+        fillcolor="#FFF3E0";
+
+        mock_api [label="Mock API\n/payments\n/preferences", fillcolor="#FFCC80"];
+        config_ui [label="Config UI\n(set responses)", fillcolor="#FFB74D"];
+        state [label="State\n(pending payments)", fillcolor="#FFA726"];
+    }
+
+    // Fake responses
+    subgraph cluster_responses {
+        label="Configurable Responses";
+        style=dashed;
+        color=gray;
+
+        approved [label="approved", fillcolor="#C8E6C9"];
+        pending [label="pending", fillcolor="#FFF9C4"];
+        rejected [label="rejected", fillcolor="#FFCDD2"];
+    }
+
+    // Real (bypassed)
+    subgraph cluster_real {
+        label="Real MercadoPago (bypassed)";
+        style=dashed;
+        color="#BDBDBD";
+
+        real_api [label="api.mercadopago.com", fillcolor="#E0E0E0", fontcolor="#9E9E9E"];
+    }
+
+    // Flow
+    backend -> mock_api [label="POST /payments"];
+    mock_api -> state [label="store"];
+    config_ui -> state [label="configure"];
+
+    state -> approved [style=dashed];
+    state -> pending [style=dashed];
+    state -> rejected [style=dashed];
+
+    mock_api -> backend [label="webhook callback", style=dashed];
+}