Replace deprecated agentBuilderToolServer and agentBuilderTriggerServer with fleetToolServer and fleetTriggerServer (#4192)

Fixes DOC-1176

## Summary

- Replaces all occurrences of the deprecated `agentBuilderToolServer`
Helm value with `fleetToolServer`
- Replaces all occurrences of the deprecated `agentBuilderTriggerServer`
Helm value with `fleetTriggerServer`
- Updates the inline Note callout that references these variable names
- Affects the `deploy-self-hosted-full-platform.mdx` page (5 total
occurrences)

## Links

- Linear:
https://linear.app/langchain/issue/DOC-1176/update-fleet-self-hosted-docs-to-replace-deprecated
- Slack:
https://langchain.slack.com/archives/C09G1T60QV9/p1779999257753749

## Verification

Verified new variable names (`fleetToolServer`, `fleetTriggerServer`)
against the LangSmith Helm chart `values.yaml` at `langchain-ai/helm`.
The deprecated names (`agentBuilderToolServer`,
`agentBuilderTriggerServer`) are no longer present in the Helm chart
values.

## Reviewers

Requested review from: @lnhsingh

---------

Co-authored-by: Docs Bot <docs-bot@langchain.dev>

Author: langsmith-fleet[bot]

src/langsmith/deploy-self-hosted-full-platform.mdx

@@ -176,10 +176,10 @@ We recommend storing each key in a predefined Kubernetes secret rather than sett
         polly:
           enabled: true
 
-        agentBuilderToolServer:
+        fleetToolServer:
           enabled: true
 
-        agentBuilderTriggerServer:
+        fleetTriggerServer:
           enabled: true
         ```
       </Tab>
@@ -199,10 +199,10 @@ We recommend storing each key in a predefined Kubernetes secret rather than sett
           enabled: true
           encryptionKey: "<polly-encryption-key>"
 
-        agentBuilderToolServer:
+        fleetToolServer:
           enabled: true
 
-        agentBuilderTriggerServer:
+        fleetTriggerServer:
           enabled: true
         ```
       </Tab>
@@ -215,7 +215,7 @@ We recommend storing each key in a predefined Kubernetes secret rather than sett
     </Warning>
 
     <Note>
-    `agentBuilderToolServer` and `agentBuilderTriggerServer` are required for Fleet.
+    `fleetToolServer` and `fleetTriggerServer` are required for Fleet. These replaced the deprecated `agentBuilderToolServer` and `agentBuilderTriggerServer` keys as of v15 of the Helm chart.
     </Note>
 
     Each feature deploys its own dedicated PostgreSQL and Redis instances by default. To use external databases instead, configure the `postgres.external` and `redis.external` sections under each feature. For example:
@@ -774,7 +774,7 @@ Setup involves creating a GitHub App, gathering its credentials, storing them as
             name: fleet-github-app
             key: state_jwt_secret
 
-    agentBuilderToolServer:
+    fleetToolServer:
       deployment:
         extraEnv:
           - name: FLEET_GITHUB_APP_ENABLED