LRC-LIB-SMARTCOLL: report saved smart albums whose rules no longer check

Rules are checked when they are made, but a saved smart album can go
bad later. The usual case is a rule testing an album that is then
deleted; it silently matches nothing.

Catalog::smart_album_problems(id) checks a saved album's rules as they
are now (RuleSet::upgrade, then RuleSet::check). It is empty for a sound
smart album, a plain album or no album. albums.list reports `problems`
for every smart album, e.g. ["rule 1: no album 8"].

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/query.rs

@@ -44,6 +44,8 @@ fn album_json(a: &Album, all: &[Album], cat: &lightcraft_catalog::Catalog) -> Va
         v["smart"] = json!(true);
         v["rules"] = serde_json::to_value(rules).unwrap_or_default();
         v["rulesText"] = json!(rules.describe());
+        // rules that no longer check (an album they test was deleted…), as `rule 1: …`
+        v["problems"] = json!(cat.smart_album_problems(a.id).iter().map(ToString::to_string).collect::<Vec<_>>());
     }
     v
 }