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/google.dot

@@ -0,0 +1,61 @@
+digraph GoogleVein {
+    rankdir=LR;
+    compound=true;
+    fontname="Helvetica";
+    node [fontname="Helvetica", fontsize=11, shape=box, style="rounded,filled"];
+    edge [fontname="Helvetica", fontsize=10];
+
+    labelloc="t";
+    label="Google Vein - OAuth Flow";
+    fontsize=16;
+
+    // Client
+    subgraph cluster_client {
+        label="Soleprint";
+        style=filled;
+        color="#E8F5E9";
+        fillcolor="#E8F5E9";
+
+        app [label="Application", fillcolor="#C8E6C9"];
+        vein [label="Google Vein\n(artery/veins/google)", fillcolor="#A5D6A7"];
+        oauth [label="OAuth Handler\n(artery/oauth.py)", fillcolor="#81C784"];
+    }
+
+    // OAuth Flow
+    subgraph cluster_oauth {
+        label="OAuth 2.0";
+        style=filled;
+        color="#FFF8E1";
+        fillcolor="#FFF8E1";
+
+        auth_url [label="1. Authorization URL", fillcolor="#FFECB3"];
+        consent [label="2. User Consent", fillcolor="#FFE082"];
+        callback [label="3. Callback + Code", fillcolor="#FFD54F"];
+        tokens [label="4. Access + Refresh\nTokens", fillcolor="#FFCA28"];
+    }
+
+    // Google APIs
+    subgraph cluster_google {
+        label="Google APIs";
+        style=filled;
+        color="#E3F2FD";
+        fillcolor="#E3F2FD";
+
+        sheets [label="Sheets API", fillcolor="#BBDEFB"];
+        calendar [label="Calendar API", fillcolor="#BBDEFB"];
+        drive [label="Drive API", fillcolor="#BBDEFB"];
+    }
+
+    // Flow
+    app -> vein [label="get_sheets()"];
+    vein -> oauth [label="ensure_auth"];
+    oauth -> auth_url;
+    auth_url -> consent;
+    consent -> callback;
+    callback -> tokens;
+    tokens -> oauth [label="store"];
+
+    oauth -> sheets [label="Bearer token"];
+    oauth -> calendar [label="Bearer token"];
+    oauth -> drive [label="Bearer token"];
+}