docs: drop AZW3 from documented format expectations

AZW3/KF8 is a proprietary legacy Amazon format (the pipeline moved to
KFX in 2015; KDP dropped MOBI-family uploads in 2022) and does not
render in the web reader. The scanner still ingests .azw/.azw3 files
(code unchanged) — they are simply no longer documented as a supported
expectation.

docs/developer/api/scanner/overview.md

@@ -30,7 +30,7 @@ The Bookhoard scanner provides comprehensive library management for ebooks, comi
 | -------- | ------------------------ |
 | EPUB     | `.epub`                  |
 | PDF      | `.pdf`                   |
-| Kindle   | `.mobi`, `.azw`, `.azw3` |
+| Kindle   | `.mobi`                  |
 | Text     | `.txt`, `.rtf`           |
 | Document | `.doc`, `.docx`          |
 | Other    | `.lit`, `.fb2`, `.pdb`   |

docs/developer/api/scanner/scan_library.md

@@ -18,7 +18,7 @@ Initiate a one-time scan of a library for ebooks, manga, or comics.
 
 The scanner automatically detects and processes files based on the library type:
 
-**Ebooks:** .epub, .pdf, .mobi, .azw, .azw3, .txt, .rtf, .doc, .docx, .lit, .fb2, .pdb
+**Ebooks:** .epub, .pdf, .mobi, .txt, .rtf, .doc, .docx, .lit, .fb2, .pdb
 
 **Comics:** .cbz, .cbr, .cb7, .cbt, .pdf