fix(backend): Zahlen im Titel sind Pflicht-Keywords, Abkuerzungen erlaubt

"700 Main Street" lud "777 Main Street" eines fremden Artists: buildTitleKeywords
behielt nur die zwei laengsten Woerter (Street, Main), die unterscheidende 700
fiel als zu kurz raus — und Schritt 3 der Kaskade prueft den Kuenstler-Channel
nicht mehr. Zahlen werden jetzt immer als \b<n>\b gefordert. Dazu eine kleine
Abkuerzungstabelle (street/st, saint/st, mount/mt, doctor/dr, versus/vs,
number/no), denn der korrekte Art Track heisst "700 Main st" und scheiterte
bisher an jedem Schritt. Tests in backend/test/ytdlp.test.js.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -64,6 +64,20 @@ Versioning: two-part `MAJOR.MINOR` — each release bumps the minor (features an
 
 ---
 
+## [Unreleased]
+
+### Fixed
+- **Downloader grabbed a same-shaped title with a different number** — searching DAT ADAM's
+  "700 Main Street" saved **"777 Main Street" by an unrelated artist**. `buildTitleKeywords` required
+  only the two longest words (Street, Main); "700" was dropped for being short, and the cascade step
+  that widens to the top 10 no longer checks the artist channel, so nothing else caught it. Numbers
+  are now always required keywords. In the same pass, a small abbreviation map (street/st, saint/st,
+  mount/mt, doctor/dr, versus/vs, number/no) lets a candidate spelled "700 Main St" match a release
+  titled "700 Main Street" — that mismatch had rejected the correct official Art Track in every step,
+  which is why the search fell through to the wrong video in the first place.
+
+---
+
 ## [2.3] — 2026-09-03
 
 A deployment-and-delivery release: production **pulls pre-built images** instead of compiling on the