Replace ASCII diagrams with Mermaid

- Add @docusaurus/theme-mermaid plugin
- Convert architecture overview diagram to Mermaid graph
- Convert heartbeat cycle to Mermaid flowchart with decision diamond
- Convert gateway lifecycle to Mermaid LR flowchart
- Convert core concepts overview diagram to Mermaid graph

Author: melvincarvalho

docs/architecture/gateway.md

@@ -73,13 +73,15 @@ openclaw gateway stop
 
 ## Process Lifecycle
 
-```
-Boot → Load Config → Initialize Memory
-  → Start WebSocket Server
-  → Connect Channels
-  → Register Skills
-  → Start Heartbeat Timer
-  → Ready (accepting connections)
+```mermaid
+flowchart LR
+    Boot["🔄 Boot"] --> Config["Load Config"]
+    Config --> Memory["Initialize\nMemory"]
+    Memory --> WS["Start WebSocket\nServer"]
+    WS --> Chan["Connect\nChannels"]
+    Chan --> Skills["Register\nSkills"]
+    Skills --> HB["Start Heartbeat\nTimer"]
+    HB --> Ready["✅ Ready\n(accepting connections)"]
 ```
 
 On shutdown, the Gateway:

docs/architecture/heartbeat.md

@@ -12,21 +12,18 @@ The Heartbeat is what transforms OpenClaw from a reactive chatbot into a **proac
 
 Every N minutes (default: 30), the Gateway triggers a heartbeat cycle:
 
-```
-┌─────────────────────────────────────┐
-│         Heartbeat Cycle              │
-│                                      │
-│  1. Timer fires (every 30 min)       │
-│  2. Gateway sends heartbeat prompt   │
-│  3. Agent reads HEARTBEAT.md         │
-│  4. Agent checks pending tasks       │
-│  5. Agent checks channel queues      │
-│  6. Decision:                        │
-│     ├─ Nothing to do → HEARTBEAT_OK  │
-│     └─ Task found → Execute + report │
-│  7. Timer resets                     │
-│                                      │
-└─────────────────────────────────────┘
+```mermaid
+flowchart TD
+    Timer["⏱️ Timer fires\n(every 30 min)"] --> Prompt["Gateway sends\nheartbeat prompt"]
+    Prompt --> ReadHB["Agent reads\nHEARTBEAT.md"]
+    ReadHB --> CheckTasks["Check pending tasks"]
+    CheckTasks --> CheckQueues["Check channel queues"]
+    CheckQueues --> Decision{"Anything\nto do?"}
+    Decision -- No --> OK["HEARTBEAT_OK\n(go back to sleep)"]
+    Decision -- Yes --> Execute["Execute task\n& report to user"]
+    OK --> Reset["Timer resets"]
+    Execute --> Reset
+    Reset -.-> Timer
 ```
 
 ## Defining Heartbeat Tasks

docs/architecture/overview.md

@@ -10,37 +10,27 @@ OpenClaw uses a **Gateway-centric architecture** where a single long-running pro
 
 ## High-Level Architecture
 
-```
-                    ┌─────────────┐
-                    │   Channels   │
-                    │  (WhatsApp,  │
-                    │  Telegram,   │
-                    │  Discord...) │
-                    └──────┬──────┘
-                           │
-                           ▼
-┌──────────────────────────────────────────────┐
-│                   Gateway                     │
-│            (ws://localhost:18789)              │
-│                                               │
-│  ┌──────────┐  ┌──────────┐  ┌────────────┐ │
-│  │  Router   │  │ Heartbeat│  │  Skill     │ │
-│  │          │  │  Timer   │  │  Registry  │ │
-│  └────┬─────┘  └────┬─────┘  └─────┬──────┘ │
-│       │              │              │         │
-│       └──────────────┼──────────────┘         │
-│                      │                         │
-│              ┌───────┴────────┐                │
-│              │  Orchestrator  │                │
-│              └───────┬────────┘                │
-│                      │                         │
-│         ┌────────────┼────────────┐            │
-│         ▼            ▼            ▼            │
-│  ┌──────────┐ ┌──────────┐ ┌──────────┐      │
-│  │  Brain   │ │  Hands   │ │  Memory  │      │
-│  │  (LLM)  │ │ (Exec)   │ │  (Local) │      │
-│  └──────────┘ └──────────┘ └──────────┘      │
-└──────────────────────────────────────────────┘
+```mermaid
+graph TD
+    Channels["🔗 Channels\n(WhatsApp, Telegram, Discord...)"]
+
+    subgraph Gateway["⚡ Gateway (ws://localhost:18789)"]
+        Router["Router"]
+        Heartbeat["Heartbeat\nTimer"]
+        SkillReg["Skill\nRegistry"]
+        Orchestrator["Orchestrator"]
+        Brain["🧠 Brain\n(LLM)"]
+        Hands["🤖 Hands\n(Exec)"]
+        Memory["💾 Memory\n(Local)"]
+    end
+
+    Channels --> Router
+    Router --> Orchestrator
+    Heartbeat --> Orchestrator
+    SkillReg --> Orchestrator
+    Orchestrator --> Brain
+    Orchestrator --> Hands
+    Orchestrator --> Memory
 ```
 
 ## Component Summary

docs/getting-started/core-concepts.md

@@ -85,28 +85,18 @@ This enables proactive behaviors like:
 
 ## How They Fit Together
 
-```
-┌─────────────────────────────────────────────┐
-│                  Gateway                     │
-│  ┌─────────┐  ┌─────────┐  ┌─────────────┐ │
-│  │  Brain   │  │  Hands  │  │  Heartbeat  │ │
-│  │  (LLM)  │←→│ (Shell, │  │  (30m loop) │ │
-│  │         │  │  Files,  │  │             │ │
-│  └────┬────┘  │ Browser) │  └──────┬──────┘ │
-│       │       └─────────┘         │         │
-│       └───────────┬───────────────┘         │
-│                   │                          │
-│  ┌────────────────┴─────────────────┐       │
-│  │            Memory                 │       │
-│  │    (~/.openclaw/memory/*.md)     │       │
-│  └──────────────────────────────────┘       │
-│                                              │
-│  ┌──────────────────────────────────┐       │
-│  │          Channels                 │       │
-│  │  WhatsApp │ Telegram │ Discord   │       │
-│  │  Slack    │ Signal   │ WebChat   │       │
-│  └──────────────────────────────────┘       │
-└─────────────────────────────────────────────┘
+```mermaid
+graph TD
+    subgraph Gateway["⚡ Gateway"]
+        Brain["🧠 Brain\n(LLM)"]
+        Hands["🤖 Hands\n(Shell, Files, Browser)"]
+        HB["⏱️ Heartbeat\n(30m loop)"]
+        Brain <--> Hands
+        Brain --- Memory["💾 Memory\n(~/.openclaw/memory/*.md)"]
+        HB --- Memory
+    end
+
+    Channels["🔗 Channels\nWhatsApp · Telegram · Discord\nSlack · Signal · WebChat"] --> Gateway
 ```
 
 ## Skills

docusaurus.config.ts

@@ -18,6 +18,12 @@ const config: Config = {
     v4: true,
   },
 
+  markdown: {
+    mermaid: true,
+  },
+
+  themes: ['@docusaurus/theme-mermaid'],
+
   i18n: {
     defaultLocale: 'en',
     locales: ['en'],