chore: Remove backup files from Git and update .gitignore

Removed from tracking:
- backup_before_pgvector_20260119.sql (database backup)
- postgres_volume_backup_20260119.tar (volume backup)
- pgvector-0.8.0.tar.gz (source archive)

Added to .gitignore:
- Database backup files (*.sql backups, *_backup_*.tar)
- Source code archives (*.tar.gz)
- Excluded Prisma migrations from .sql ignore rule

.gitignore

@@ -48,6 +48,20 @@ tmp/
 temp/
 *.tmp
 
+# Database backups (large files, backup locally only)
+*.sql
+!backend/prisma/migrations/**/*.sql
+!backend/prisma/manual-migrations/**/*.sql
+!backend/scripts/**/*.sql
+backup_*.sql
+*_backup_*.sql
+*_backup_*.tar
+postgres_volume_backup_*.tar
+
+# Source code archives
+*.tar.gz
+pgvector-*.tar.gz
+
 # Backend uploads (用户上传的文件，不应提交到Git)
 backend/uploads/