Address Trenly's review feedback

- Update Pre* field descriptions to 'Confirmation request displayed'
  to clarify they invoke a user prompt
- Fix inconsistency: reference userMessages.disablePostActionMessages
  setting instead of disableInstallNotes for post-action suppression

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: denelon

doc/specs/#3483 - UserMessages.md

@@ -38,7 +38,7 @@ A new optional `UserMessages` object is added to the **defaultLocale** and **loc
             "type": ["string", "null"],
             "minLength": 1,
             "maxLength": 2048,
-            "description": "Message displayed to the user before a package installation begins."
+            "description": "Confirmation request displayed to the user before a package installation begins."
         },
         "PostInstall": {
             "type": ["string", "null"],
@@ -50,7 +50,7 @@ A new optional `UserMessages` object is added to the **defaultLocale** and **loc
             "type": ["string", "null"],
             "minLength": 1,
             "maxLength": 2048,
-            "description": "Message displayed to the user before a package upgrade begins."
+            "description": "Confirmation request displayed to the user before a package upgrade begins."
         },
         "PostUpgrade": {
             "type": ["string", "null"],
@@ -62,7 +62,7 @@ A new optional `UserMessages` object is added to the **defaultLocale** and **loc
             "type": ["string", "null"],
             "minLength": 1,
             "maxLength": 2048,
-            "description": "Message displayed to the user before a package uninstall begins."
+            "description": "Confirmation request displayed to the user before a package uninstall begins."
         },
         "PostUninstall": {
             "type": ["string", "null"],
@@ -139,7 +139,7 @@ Successfully installed ExampleApp [Publisher.ExampleApp] v2.0.0
   Restart your terminal to use the CLI.
 ```
 
-Post-action messages are displayed in both interactive and non-interactive modes. They are suppressed when the `disableInstallNotes` setting is enabled (extended to cover all post-action messages, not just `InstallationNotes`).
+Post-action messages are displayed in both interactive and non-interactive modes. They are suppressed when the `userMessages.disablePostActionMessages` setting is enabled.
 
 #### Flow Behavior Matrix