feat(core): score season packs per episode

A size band describes one episode (DESIGN.md §5.5), so both the target
penalty and the floor now compare a release's size divided by the number
of episodes it covers. The caller supplies the count — arr-core has no
IO. Movies and unknown counts divide by one, so movie scoring is
unchanged and pinned by test.

Closes #180

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

crates/arr-db/src/policy.rs

@@ -619,7 +619,12 @@ mod tests {
 
         let one_and_a_half_gib = 1536 << 20;
         assert_eq!(
-            arr_core::score::is_below_floor(&loaded.policy, Resolution::R1080p, one_and_a_half_gib),
+            arr_core::score::is_below_floor(
+                &loaded.policy,
+                Resolution::R1080p,
+                one_and_a_half_gib,
+                1
+            ),
             Some(false)
         );
     }