Update documentation to reflect interactive rating system and API changes

- Update README.md with interactive rating system details
- Document zero-rating behavior in GET /api/ebooks/:id/rating
- Add comprehensive rating system documentation section
- Update Bruno collection files to reflect new API behavior
- Enhance API testing documentation with rating 0 fallback

bruno/ebooks/Get Ebook Rating.bru

@@ -25,7 +25,7 @@ docs {
   **Path Parameters:**
   - `id` (string): Ebook UUID
 
-  **Response:**
+  **Response when rating exists:**
   - `id` (string): Rating UUID
   - `ebook_id` (string): Ebook UUID
   - `user_id` (string): User UUID
@@ -33,7 +33,13 @@ docs {
   - `created_at` (string): Creation timestamp
   - `updated_at` (string): Last update timestamp
 
+  **Response when no rating exists:**
+  - `ebook_id` (string): Ebook UUID
+  - `user_id` (string): User UUID
+  - `rating` (number): Always 0 (indicates no rating)
+
   **Error Responses:**
   - 401: Invalid authentication
-  - 404: Rating not found
+  
+  **Note:** This endpoint returns HTTP 200 with rating 0 when no rating exists, instead of HTTP 404.
 }