fix: match the compact edition markers a cover carries

"Building Microservices, 2E" never matched "Building Microservices". Key the
strip on the trailing "e" so 2E, 5e and 3 Ed are caught, while a bare number
leaves "Catch 22" and "Blade Runner 2049" alone. Stored keys are recomputed.

backend/tests/unit/test_matching.py

@@ -30,6 +30,11 @@ class TestNormalizeTitle:
             ("Frankenstein (Illustrated)", "frankenstein"),
             ("Frankenstein [Kindle Edition]", "frankenstein"),
             ("Frankenstein, 2nd Edition", "frankenstein"),
+            # The compact forms a cover actually carries.
+            ("Building Microservices, 2E", "building microservices"),
+            ("Building Microservices 2e", "building microservices"),
+            ("Frankenstein 3 Ed", "frankenstein"),
+            ("Dungeons & Dragons 5e", "dungeons and dragons"),
             ("Frankenstein Revised Edition", "frankenstein"),
             ("Dune Deluxe Edition Illustrated", "dune"),
             ("", ""),
@@ -47,6 +52,13 @@ class TestNormalizeTitle:
         """An article-only title is not improved by having no article left."""
         assert normalize_title("The") == "the"
 
+    @pytest.mark.parametrize(
+        "title", ["Catch 22", "Fahrenheit 451", "Blade Runner 2049", "1984", "Apollo 13"]
+    )
+    def test_a_number_is_not_an_edition(self, title: str) -> None:
+        """Edition stripping keys on the `e`; a bare number is part of the title."""
+        assert normalize_title(title) == title.casefold()
+
 
 
 class TestNormalizeAuthor: