refactor(bruno): standardize all variables to snake_case naming convention

Standardize all Bruno environment variables to use snake_case convention
(aligned with Go naming practices) and remove duplicate camelCase variants.

Changes:
- Environment file cleanup:
  - Remove: baseUrl, ebookid, fakebookid, libraryId, mediaItemId, isVisible, refreshToken
  - Standardize: fakebookid → fake_book_id, isVisible → is_visible, refreshToken → refresh_token
  - All variables now use consistent snake_case format

- Update all Bruno requests to use standardized variables:
  - ebooks: {{ebookid}} → {{ebook_id}}
  - library: {{libraryId}} → {{library_id}}
  - media-items: {{mediaItemId}} → {{media_item_id}}
  - visibility: {{isVisible}} → {{is_visible}}
  - auth: {{refreshToken}} → {{refresh_token}}

Benefits:
- Single source of truth for each variable
- Consistent with Go naming conventions
- No ambiguity about which variable name to use
- Cleaner, more maintainable codebase

bruno/user/auth/Logout User.bru

@@ -16,12 +16,12 @@
     "body": {
       "type": "json",
       "json": {
-        "refresh_token": "{{refreshToken}}"
+        "refresh_token": "{{refresh_token}}"
       }
     },
     "url": {
-      "raw": "{{baseUrl}}/api/auth/logout",
-      "host": ["{{baseUrl}}"],
+      "raw": "{{base_url}}/api/auth/logout",
+      "host": ["{{base_url}}"],
       "path": ["api", "auth", "logout"]
     },
     "description": "Logs out the user by revoking their refresh token. If no refresh token is provided, the request succeeds but no token is revoked."
@@ -39,8 +39,8 @@
           }
         },
         "url": {
-          "raw": "{{baseUrl}}/api/auth/logout",
-          "host": ["{{baseUrl}}"],
+          "raw": "{{base_url}}/api/auth/logout",
+          "host": ["{{base_url}}"],
           "path": ["api", "auth", "logout"]
         }
       },
@@ -65,8 +65,8 @@
           "json": {}
         },
         "url": {
-          "raw": "{{baseUrl}}/api/auth/logout",
-          "host": ["{{baseUrl}}"],
+          "raw": "{{base_url}}/api/auth/logout",
+          "host": ["{{base_url}}"],
           "path": ["api", "auth", "logout"]
         }
       },

bruno/user/auth/Refresh Token.bru

@@ -16,12 +16,12 @@
     "body": {
       "type": "json",
       "json": {
-        "refresh_token": "{{refreshToken}}"
+        "refresh_token": "{{refresh_token}}"
       }
     },
     "url": {
-      "raw": "{{baseUrl}}/api/auth/refresh",
-      "host": ["{{baseUrl}}"],
+      "raw": "{{base_url}}/api/auth/refresh",
+      "host": ["{{base_url}}"],
       "path": ["api", "auth", "refresh"]
     },
     "description": "Refreshes an access token using a valid refresh token. Returns a new access token with 1-hour expiration."
@@ -39,8 +39,8 @@
           }
         },
         "url": {
-          "raw": "{{baseUrl}}/api/auth/refresh",
-          "host": ["{{baseUrl}}"],
+          "raw": "{{base_url}}/api/auth/refresh",
+          "host": ["{{base_url}}"],
           "path": ["api", "auth", "refresh"]
         }
       },
@@ -67,8 +67,8 @@
           }
         },
         "url": {
-          "raw": "{{baseUrl}}/api/auth/refresh",
-          "host": ["{{baseUrl}}"],
+          "raw": "{{base_url}}/api/auth/refresh",
+          "host": ["{{base_url}}"],
           "path": ["api", "auth", "refresh"]
         }
       },