refactor(bruno): reorganize file structure from bruno-yaml to flat bruno directory

- Move all files from bruno-yaml/* to bruno/*
- Maintains existing directory structure within categories
- Updates bruno/user/auth files with OAuth2 refresh token flow
- Updates bruno/user/profile files for user profile management
- Adds bruno/dashboard/ directory with dashboard API tests
- Preserves all existing test scenarios and OpenCollection YAML format
- No functional changes - file reorganization only

bruno/user/profile/Update Username.yml

@@ -0,0 +1,33 @@
+info:
+  name: Update Username
+  type: http
+  seq: 1
+http:
+  method: PUT
+  url: '{{base_url}}/api/auth/username'
+  auth: inherit
+  body:
+    type: json
+
+docs: |-
+  ## Update Username
+  
+    Updates the authenticated user's username.
+  
+    **Method:** PUT
+  
+     **Endpoint:** /api/auth/username
+  
+    **Authentication:** Required
+  
+    **Request Body:**
+    - `username` (string, required): New username (3-50 characters)
+  
+    **Response:**
+    - `message` (string): Success message
+  
+    **Status Codes:**
+    - 200: Success
+    - 400: Invalid username
+    - 401: Unauthorized
+    - 409: Username already taken