fix(downloads): Facebook files get their upload date, non-Latin names their letters

Since 2026-10-28 the signed-in Facebook read gives no upload date, so
every Facebook file since was named 0000-00-00 in Season_0 (31 on prod,
none before). The signed-out read that already titles these downloads
carries the date, so it now lends that too when the signed-in read has
none (backfill.public_title_info is now public_page_info).

On-disk names dropped every letter outside the Latin script, so a Hebrew,
Cyrillic, Greek or CJK uploader went to one shared "untitled" folder
(prod asset 503). anyascii now writes them in Latin letters
(Сергей Иванов -> Sergei_Ivanov); Latin and accented names are unchanged.

backend/tests/test_naming.py

@@ -26,9 +26,21 @@ def test_sanitize_output_is_pure_ascii_without_spaces():
         assert _is_ascii_slug(out), out
 
 
-def test_sanitize_non_latin_falls_back_not_crashes():
-    # A title with no ASCII base collapses to the untitled fallback rather than an empty name.
-    assert storage.sanitize("日本語") == "untitled"
+def test_sanitize_writes_a_non_latin_name_in_latin_letters():
+    # Prod asset 503: a Hebrew uploader name was dropped whole, so the file went to "untitled/", the
+    # folder every Hebrew, Cyrillic, Greek or CJK name would share — one show in Plex for all of them.
+    names = ("מַלכָּה אָדוֹם", "Сергей Иванов", "Ελληνικά Νέα", "日本語", "محمد علي")
+    slugs = [storage.sanitize(n) for n in names]
+    for name, slug in zip(names, slugs, strict=True):
+        assert _is_ascii_slug(slug) and slug != "untitled", (name, slug)
+    assert len(set(slugs)) == len(slugs), slugs  # two names, two folders
+    # The measured spellings (anyascii 0.3.3, the locked one).
+    assert slugs == ["mlkhh_dvm", "Sergei_Ivanov", "Ellinika_Nea", "RiBenYu", "mhmd_ly"]
+
+
+def test_sanitize_falls_back_when_nothing_is_left():
+    # Emoji and symbols are dropped, and a name of nothing else still gets a folder.
+    assert storage.sanitize("🎉🎉") == "untitled"
 
 
 def test_display_filename_uses_underscores_and_ascii():