style: enhance README diagrams with improved subgraph labels and node styling for clarity

packages/core-events/README.md

@@ -20,7 +20,7 @@ By routing communication through a centralized event bus, we achieve:
 
 ```mermaid
 graph TD
-    subgraph "@repo/core-events (Pure Tool)"
+    subgraph Core ["@repo/core-events (Pure Tool)"]
         R["AppEventRegistry<br/>(empty interface)"]
         T["AppEvents = mapped type"]
         E((Event Bus<br/>mitt))
@@ -29,7 +29,7 @@ graph TD
         E --> H
     end
 
-    subgraph "apps/web (App Autonomy)"
+    subgraph Apps ["apps/web (App Autonomy)"]
         D["events.d.ts<br/>declare module augmentation"]
         A[Cashier UI]
         B[Profile Settings]
@@ -49,9 +49,24 @@ graph TD
     E -.-> Y
     E -.-> Z
 
-    style E fill:#4263eb,color:#fff,stroke:#fff
-    style R fill:#2b8a3e,color:#fff,stroke:#fff
-    style D fill:#e67700,color:#fff,stroke:#fff
+    %% Styling Subgraphs (Backgrounds)
+    style Core fill:#f8f9fa,stroke:#ced4da,stroke-width:2px,color:#495057
+    style Apps fill:#e7f5ff,stroke:#74c0fc,stroke-width:2px,color:#1864ab
+
+    %% Styling Core Engine (Purple) & Contracts (Green)
+    style R fill:#20c997,stroke:#089981,color:#fff
+    style T fill:#20c997,stroke:#089981,color:#fff
+    style E fill:#845ef7,stroke:#5f3dc4,color:#fff
+    style H fill:#845ef7,stroke:#5f3dc4,color:#fff
+
+    %% Styling App Injection (Orange) & Components (Blue)
+    style D fill:#fd7e14,stroke:#d9480f,color:#fff
+    style A fill:#339af0,stroke:#1864ab,color:#fff
+    style B fill:#339af0,stroke:#1864ab,color:#fff
+    style C fill:#339af0,stroke:#1864ab,color:#fff
+    style X fill:#339af0,stroke:#1864ab,color:#fff
+    style Y fill:#339af0,stroke:#1864ab,color:#fff
+    style Z fill:#339af0,stroke:#1864ab,color:#fff
 ```
 
 ---