fix(meta): store unrated titles as NULL, not zero

TMDB reports vote_average: 0 where no rating exists (#156). Normalise
it to None at the arr-meta edge, like non_empty does for "", and let
the Option flow through the daemon refresh and API add paths so the
nullable columns from #145 do their job.

crates/arr-meta/src/model.rs

@@ -82,8 +82,10 @@ pub struct Movie {
     /// Path fragment, not a URL. §9.6 stores this on the row alongside
     /// [`Movie::poster_path`] and `vote_average`.
     pub backdrop_path: Option<String>,
-    /// TMDB's rating, out of 10. Stored with the artwork (§9.6).
-    pub vote_average: f64,
+    /// TMDB's rating, out of 10, when TMDB has votes for it. Stored with the
+    /// artwork (§9.6). TMDB sends `0` where "no rating yet" is meant, so a
+    /// zero rating is normalised away here rather than stored as one.
+    pub vote_average: Option<f64>,
 }
 
 impl Movie {
@@ -136,8 +138,9 @@ pub struct Series {
     /// §9.6 stores this on the row alongside `poster_path` and
     /// [`Series::vote_average`].
     pub backdrop_path: Option<String>,
-    /// TMDB's rating, out of 10. Stored with the artwork (§9.6).
-    pub vote_average: f64,
+    /// TMDB's rating, out of 10, when TMDB has votes for it. Stored with the
+    /// artwork (§9.6); zero is normalised away like [`Movie::vote_average`].
+    pub vote_average: Option<f64>,
     pub seasons: Vec<SeasonSummary>,
 }
 
@@ -372,7 +375,7 @@ impl From<RawSeries> for Series {
             overview: non_empty(raw.overview),
             poster_path: non_empty(raw.poster_path),
             backdrop_path: non_empty(raw.backdrop_path),
-            vote_average: raw.vote_average,
+            vote_average: rating(raw.vote_average),
             seasons: raw
                 .seasons
                 .into_iter()
@@ -562,7 +565,7 @@ impl From<RawMovie> for Movie {
             overview: non_empty(raw.overview),
             poster_path: non_empty(raw.poster_path),
             backdrop_path: non_empty(raw.backdrop_path),
-            vote_average: raw.vote_average,
+            vote_average: rating(raw.vote_average),
         }
     }
 }
@@ -596,6 +599,12 @@ fn non_empty(value: Option<String>) -> Option<String> {
     value.filter(|text| !text.is_empty())
 }
 
+/// TMDB uses `0` where "no votes yet" is meant, so an unrated title never
+/// carries a rating rather than carrying zero.
+fn rating(value: f64) -> Option<f64> {
+    (value != 0.0).then_some(value)
+}
+
 #[derive(Debug, Deserialize)]
 pub(crate) struct RawMovieDetail {
     id: u32,

crates/arr-meta/tests/tmdb.rs

@@ -217,6 +217,9 @@ async fn unreleased_movie_has_no_dates_and_no_imdb_id() {
     assert_eq!(movie.imdb_id, None);
     assert_eq!(movie.runtime, None);
     assert!(movie.origin_countries.is_empty());
+    // TMDB reports vote_average: 0 for an unrated title — absence, not zero
+    // (#156), so it is normalised away like any other zero-valued null.
+    assert_eq!(movie.vote_average, None);
     assert!(!movie.is_digitally_released(date(2026, 8, 22)));
 }