chore: ignore fictional characters XLSX and PDF file in packs

- Added packs/warbler-pack-kh-fict-chars/fictional_characters.xlsx to .gitignore
- Added packs/warbler-pack-pdf/TheSilverWyvernsEvening.pdf to .gitignore

These appear to be data files for specific packs and should not be tracked in version control to avoid repository bloat.

.gitignore

@@ -127,3 +127,5 @@ models/
 packs/warbler-pack-kh-tinystories/train.csv
 packs/warbler-pack-kh-tinystories/validation.csv
 packs/warbler-pack-kh-tinystories/train.csv
+packs/warbler-pack-kh-fict-chars/fictional_characters.xlsx
+packs/warbler-pack-pdf/TheSilverWyvernsEvening.pdf