docs: final fix for mermaid participant naming

- Remove quotes from Backend (Upstream) participant for consistency
- All participants now properly match throughout the diagram
- Maintains line breaks to prevent text overflow

Author: desimone

content/docs/reference/global-timeouts.mdx

@@ -31,12 +31,12 @@ The following diagram shows how different timeouts apply throughout the request
 sequenceDiagram
     participant Client
     participant Pomerium
-    participant "Backend (Upstream)"
+    participant Backend (Upstream)
     Client->>Pomerium: HTTP Request (from client)
     Note over Client,Pomerium: Read Timeout starts when request begins
-    Pomerium->>"Backend (Upstream)": Forward request to upstream<br/>(once request is fully received)
-    Note over Pomerium,"Backend (Upstream)": Default Upstream Timeout starts<br/>after full request is received
-    "Backend (Upstream)"-->>Pomerium: Upstream Response
+    Pomerium->>Backend (Upstream): Forward request to upstream<br/>(once request is fully received)
+    Note over Pomerium,Backend (Upstream): Default Upstream Timeout starts<br/>after full request is received
+    Backend (Upstream)-->>Pomerium: Upstream Response
     Pomerium-->>Client: HTTP Response (to client)
     Note over Pomerium,Client: Write Timeout covers<br/>entire request+response stream
     Note right of Pomerium: Idle Timeout closes idle connections<br/>with no active requests