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/slack.dot

@@ -0,0 +1,64 @@
+digraph SlackVein {
+    rankdir=LR;
+    compound=true;
+    fontname="Helvetica";
+    node [fontname="Helvetica", fontsize=11, shape=box, style="rounded,filled"];
+    edge [fontname="Helvetica", fontsize=10];
+
+    labelloc="t";
+    label="Slack Vein - API Flow";
+    fontsize=16;
+
+    // Client
+    subgraph cluster_client {
+        label="Soleprint";
+        style=filled;
+        color="#E8F5E9";
+        fillcolor="#E8F5E9";
+
+        app [label="Application", fillcolor="#C8E6C9"];
+        vein [label="Slack Vein\n(artery/veins/slack)", fillcolor="#A5D6A7"];
+    }
+
+    // Auth
+    subgraph cluster_auth {
+        label="Authentication";
+        style=filled;
+        color="#FFF8E1";
+        fillcolor="#FFF8E1";
+
+        token [label="Bot Token\n(Bearer)", fillcolor="#FFECB3"];
+    }
+
+    // Slack API
+    subgraph cluster_slack {
+        label="Slack API";
+        style=filled;
+        color="#E3F2FD";
+        fillcolor="#E3F2FD";
+
+        chat [label="chat.postMessage", fillcolor="#BBDEFB"];
+        channels [label="conversations.list", fillcolor="#BBDEFB"];
+        users [label="users.list", fillcolor="#BBDEFB"];
+        files [label="files.upload", fillcolor="#BBDEFB"];
+    }
+
+    // Webhooks
+    subgraph cluster_webhooks {
+        label="Incoming";
+        style=dashed;
+        color=gray;
+
+        webhook [label="Webhook URL", fillcolor="#F5F5F5"];
+    }
+
+    // Flow
+    app -> vein [label="send_message()"];
+    vein -> token [label="auth"];
+    token -> chat [label="POST"];
+    token -> channels [label="GET"];
+    token -> users [label="GET"];
+    token -> files [label="POST"];
+
+    vein -> webhook [label="simple post", style=dashed];
+}