Replace text diagrams with mermaid (#7165)

* Replace text diagrams with mermaid

* Fix review comments

* Remove newlines

* docs: fix mermaid prep blockers (#7165)

---------

Co-authored-by: Sebastian <19554889+sebslight@users.noreply.github.com>

docs/gateway/security/index.md

@@ -797,21 +797,33 @@ Commit the updated `.secrets.baseline` once it reflects the intended state.
 
 ## The Trust Hierarchy
 
-```
-Owner (Peter)
-  │ Full trust
-  ▼
-AI (Clawd)
-  │ Trust but verify
-  ▼
-Friends in allowlist
-  │ Limited trust
-  ▼
-Strangers
-  │ No trust
-  ▼
-Mario asking for find ~
-  │ Definitely no trust 😏
+```mermaid
+%%{init: {
+  'theme': 'base',
+  'themeVariables': {
+    'primaryColor': '#ffffff',
+    'primaryTextColor': '#000000',
+    'primaryBorderColor': '#000000',
+    'lineColor': '#000000',
+    'secondaryColor': '#f9f9fb',
+    'tertiaryColor': '#ffffff',
+    'clusterBkg': '#f9f9fb',
+    'clusterBorder': '#000000',
+    'nodeBorder': '#000000',
+    'mainBkg': '#ffffff',
+    'edgeLabelBackground': '#ffffff'
+  }
+}}%%
+flowchart TB
+    A["Owner (Peter)"] -- Full trust --> B["AI (Clawd)"]
+    B -- Trust but verify --> C["Friends in allowlist"]
+    C -- Limited trust --> D["Strangers"]
+    D -- No trust --> E["Mario asking for find ~"]
+    E -- Definitely no trust 😏 --> F[" "]
+
+     %% The transparent box is needed to show the bottom-most label correctly
+     F:::Class_transparent_box
+    classDef Class_transparent_box fill:transparent, stroke:transparent
 ```
 
 ## Reporting Security Issues