Update competitive matrix and migration pages (#138)

## Competitive Matrix Changes

| Competitor | Capability | Change |
| --- | --- | --- |
| VidaiMock | Image generation | No -> Yes |
| VidaiMock | Structured output / JSON mode | No -> Yes |
| VidaiMock | Sequential / stateful responses | No -> Yes |
| VidaiMock | Drift detection | No -> Yes |
| VidaiMock | Request journal | No -> Yes |
| piyook/llm-mock | GitHub Action | No -> Yes |
| mokksy/ai-mocks | GitHub Action | No -> Yes |

```mermaid
flowchart LR
  subgraph VidaiMock["VidaiMock"]
    n0["Image generation"]
    n1["Structured output / JSON mode"]
    n2["Sequential / stateful responses"]
    n3["Drift detection"]
    n4["Request journal"]
  end
  subgraph piyook_llm-mock["piyook/llm-mock"]
    n5["GitHub Action"]
  end
  subgraph mokksy_ai-mocks["mokksy/ai-mocks"]
    n6["GitHub Action"]
  end
```

Author: jpr5

docs/index.html

@@ -1637,7 +1637,7 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td>Image generation</td>
                 <td class="col-aimock"><span class="yes">Built-in &#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
@@ -1727,7 +1727,7 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td>Drift detection</td>
                 <td class="col-aimock"><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
@@ -1736,7 +1736,7 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td>Sequential / stateful responses</td>
                 <td class="col-aimock"><span class="yes">Built-in &#10003;</span></td>
                 <td><span class="manual">manual</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
                 <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
@@ -1745,7 +1745,7 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td>Request journal</td>
                 <td class="col-aimock"><span class="yes">&#10003;</span></td>
                 <td><span class="manual">manual</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
@@ -1781,7 +1781,7 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td>Structured output / JSON mode</td>
                 <td class="col-aimock"><span class="yes">Built-in &#10003;</span></td>
                 <td><span class="manual">manual</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
@@ -1810,8 +1810,8 @@ <h2 class="fade-in">How aimock compares</h2>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
                 <td><span class="no">&#10007;</span></td>
-                <td><span class="no">&#10007;</span></td>
-                <td><span class="no">&#10007;</span></td>
+                <td><span class="yes">&#10003;</span></td>
+                <td><span class="yes">&#10003;</span></td>
               </tr>
               <tr>
                 <td>Vitest / Jest plugins</td>