Refactor: rename baseUrl to base_url in .bru files

Update configuration key naming convention to use snake_case
consistently.
Applies changes recursively across all subdirectories.

bruno/analytics/Get Device Usage.bru

@@ -5,7 +5,7 @@ meta {
 }
 
 get {
-  url: {{baseUrl}}/api/analytics/device-usage
+  url: {{base_url}}/api/analytics/device-usage
   body: none
   auth: inherit
 }

bruno/analytics/Get Popular Books.bru

@@ -5,7 +5,7 @@ meta {
 }
 
 get {
-  url: {{baseUrl}}/api/analytics/popular-books?limit=10
+  url: {{base_url}}/api/analytics/popular-books?limit=10
   body: none
   auth: inherit
 }

bruno/analytics/Get Reading Stats Date Range.bru

@@ -5,7 +5,7 @@ meta {
 }
 
 get {
-  url: {{baseUrl}}/api/analytics/reading-stats?start_date=2024-01-01&end_date=2024-01-31
+  url: {{base_url}}/api/analytics/reading-stats?start_date=2024-01-01&end_date=2024-01-31
   body: none
   auth: inherit
 }

bruno/analytics/Get Reading Stats.bru

@@ -5,7 +5,7 @@ meta {
 }
 
 get {
-  url: {{baseUrl}}/api/analytics/reading-stats
+  url: {{base_url}}/api/analytics/reading-stats
   body: none
   auth: inherit
 }