docs(bruno): update API test files for media terminology

- Rename ebook_id environment variable to media_item_id
- Update scanner endpoint example paths and documentation
- Update library endpoint documentation
- Keep library type 'ebooks' where appropriate (valid type value)

bruno/environments/Bookmann.bru

@@ -1,9 +1,8 @@
 vars {
   base_url: http://localhost:8765
-  ebook_id: 02a535a4-19f8-43fa-b81b-89a226d19dd9
+  media_item_id: 02a535a4-19f8-43fa-b81b-89a226d19dd9
   fake_book_id: 123e4567-e89b-12d3-a456-426614174000
   user_id: c51118f0-31fc-4c32-827d-517d6599bf21
-  media_item_id: 550e8400-e29b-41d4-a716-446655440000
   highlight_id: 660f9501-f29b-51d4-b716-446655440001
   note_id: 7710a602-g29b-61d4-c716-446655440002
   library_id: cc23c3a7-f8fb-451a-a78d-2a16df1b725a

bruno/library/Update Scan Settings.bru

@@ -29,7 +29,7 @@ settings {
 docs {
   ## Update Scan Settings
   
-  Updates the user's ebook scanning settings.
+  Updates the user's media scanning settings.
   
   **Method:** PUT
   

bruno/scanner/Scan Media Items.bru

@@ -17,7 +17,7 @@ settings {
 
 body:json {
   {
-    "folder_paths": ["/path/to/ebooks"]
+    "folder_paths": ["/path/to/media"]
   }
 }
 

bruno/scanner/Start Watch Mode.bru

@@ -41,7 +41,7 @@ docs {
   
   **How it works:**
   - Monitors all folders configured for the library
-  - Automatically detects new ebook files (CREATE events)
+  - Automatically detects new media files (CREATE events)
   - Detects modifications to existing files (WRITE events)
   - Processes new files within milliseconds of detection
   - Automatically watches new subdirectories as they're created