fix: address second code review findings

- Add CacheTTL default (24h) in config applyDefaults — without this,
  omitting cache_ttl from config silently defeats the entire caching
  mechanism (TTL=0 means cached data is never served)
- Fix pagination to use total Count instead of checking if last page
  was short — avoids wasting a rate-limit token when total count is
  an exact multiple of 100
- Preserve user-set IsIgnored flags across re-syncs — previously,
  DELETE+INSERT in the sync transaction reset all ignore flags to
  false, losing user preferences on every cache-expiry re-sync
- Check context cancellation on cache-hit code path — previously,
  ctx.Err() was not checked between cache check and returning cached
  data, violating the cancellation contract

internal/config/config.go

@@ -86,6 +86,9 @@ func applyDefaults(cfg *Config) {
 	if cfg.Scanner.FuzzyThreshold == 0 {
 		cfg.Scanner.FuzzyThreshold = 0.85
 	}
+	if cfg.MusicBrainz.CacheTTL == 0 {
+		cfg.MusicBrainz.CacheTTL = 24 * time.Hour
+	}
 }
 
 // validate checks that required fields are set and values are within acceptable ranges.