docs: use ASCII-only diagram for consistent rendering

Author: chaodu-agent

docs/refarch/aws-ecs-fargate-spot.md

@@ -13,30 +13,30 @@ Deploy a single OpenAB bot on ECS Fargate Spot for ~$2.7/month with persistent a
 ## Architecture
 
 ```
-┌─ AWS ─────────────────────────────────────────────────────┐
-│                                                           │
-│  ┌─ ECS Fargate Spot Task ─────────────────────────────┐  │
-│  │                                                     │  │
-│  │  ┌───────────┐ ┌────────────────┐ ┌────────────┐   │  │
-│  │  │s3-restore │ │    openab      │ │  s3-sync   │   │  │
-│  │  │(init)     │→│(main container)│ │ (sidecar)  │   │  │
-│  │  │pull auth  │ │ kiro-cli acp   │ │ push auth  │   │  │
-│  │  │from S3    │ │ Discord bot    │ │ every 5min │   │  │
-│  │  └───────────┘ └────────────────┘ └────────────┘   │  │
-│  │       ↑             ↑      ↑            ↑          │  │
-│  │       └─────────────┴ /data volume ─────┘          │  │
-│  └─────────────────────────────────────────────────────┘  │
-│                                                           │
-│      ↕                     ↕                              │
-│  S3 Bucket           Secrets Manager                      │
-│  (auth state)         (bot token)                         │
-│                                                           │
-└───────────────────────────────────────────────────────────┘
-                            ↕               ↕
-                       Discord API   ┌─ GitHub ──────┐
-                      (bot gateway)  │ Gist          │
-                                     │ (config.toml) │
-                                     └───────────────┘
++-- AWS -------------------------------------------------------+
+|                                                              |
+|  +-- ECS Fargate Spot Task --------------------------------+ |
+|  |                                                         | |
+|  |  +-----------+  +----------------+  +------------+      | |
+|  |  |s3-restore |  |    openab      |  |  s3-sync   |      | |
+|  |  |(init)     |->|(main container)|  | (sidecar)  |      | |
+|  |  |pull auth  |  | kiro-cli acp   |  | push auth  |      | |
+|  |  |from S3    |  | Discord bot    |  | every 5min |      | |
+|  |  +-----------+  +----------------+  +------------+      | |
+|  |       |              |      |            |              | |
+|  |       +--------------+- /data volume ----+              | |
+|  +---------------------------------------------------------+ |
+|                                                              |
+|      |                     |                                 |
+|  S3 Bucket           Secrets Manager                         |
+|  (auth state)         (bot token)                            |
+|                                                              |
++--------------------------------------------------------------+
+                            |               |
+                       Discord API   +-- GitHub ------+
+                      (bot gateway)  | Gist           |
+                                     | (config.toml)  |
+                                     +----------------+
 ```
 
 ## Cost