fix: merge main (v0.161.0) into classification feature branch

Resolve all 40 merge conflicts from merging origin/main into the
classification feature branch. Key resolutions:

- Auto-generated files (BUILD_DATE, VERSION, etc.): use main's version
- API tokens: take main's version (token expiry, reactivation, hard-delete)
- Auth: take main's Dropbox credential sharing + token expiry checking
- Config: take main's social_auth_dropbox_use_global_credentials option
- Files API: take main's improved duplicate handling + rate limiting
- Models: keep ClassificationRuleModel alongside main's new models
- Mobile: take main's mature implementation
- Templates/translations: take main's versions (device deletion, reactivation keys)
- Migration: renumber 038_add_classification_rules → 039_add_classification_rules
  to chain after main's 038_add_api_token_expires_at
- Requirements: take main's version (adds segno QR library)
- Tests: take main's more complete token tests, keep classification imports

app/tasks/convert_to_pdf.py

@@ -205,7 +205,7 @@ def convert_to_pdf(
         ".pdf",  # PDF (already in PDF format but can be processed)
     }
 
-    IMAGE_EXTENSIONS = {".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tiff", ".tif", ".webp", ".svg"}
+    IMAGE_EXTENSIONS = {".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tiff", ".tif", ".webp", ".svg", ".heic", ".heif"}
 
     HTML_EXTENSIONS = {".html", ".htm"}