feat(admin): enable 30 day default retention for chat history & remove warning (#20853)

docs/reference/configuration.md

@@ -159,12 +159,12 @@ their corresponding top-level category object in your `settings.json` file.
 
 - **`general.sessionRetention.enabled`** (boolean):
   - **Description:** Enable automatic session cleanup
-  - **Default:** `false`
+  - **Default:** `true`
 
 - **`general.sessionRetention.maxAge`** (string):
   - **Description:** Automatically delete chats older than this time period
     (e.g., "30d", "7d", "24h", "1w")
-  - **Default:** `undefined`
+  - **Default:** `"30d"`
 
 - **`general.sessionRetention.maxCount`** (number):
   - **Description:** Alternative: Maximum number of sessions to keep (most
@@ -175,11 +175,6 @@ their corresponding top-level category object in your `settings.json` file.
   - **Description:** Minimum retention period (safety limit, defaults to "1d")
   - **Default:** `"1d"`
 
-- **`general.sessionRetention.warningAcknowledged`** (boolean):
-  - **Description:** INTERNAL: Whether the user has acknowledged the session
-    retention warning
-  - **Default:** `false`
-
 #### `output`
 
 - **`output.format`** (enum):