test(e2e): cross-process harness over the §12 seams (#66)

crates/arr-api/src/state.rs

@@ -52,7 +52,8 @@ impl Upstreams {
         self
     }
 
-    /// Point TMDB somewhere other than the real API. Tests only.
+    /// Point TMDB somewhere other than the real API. Tests and the
+    /// `ARR_TMDB_URL` e2e seam only.
     #[must_use]
     pub fn with_tmdb_url(mut self, url: String) -> Self {
         self.tmdb_url = url;