deprecate k-tv-backend, fix workspace feature-unification build

crates/mcp/src/main.rs

@@ -127,6 +127,7 @@ fn wire_repositories(pool: &DbPool) -> anyhow::Result<WireOutput> {
                 library_query: w.library_query,
             })
         }
+        _ => anyhow::bail!("database backend not compiled into this binary"),
     }
 }