fix: address code review findings

Remove dead code: duplicate ExternalRelease/Artist/ParsedArtist structs in
model.go, ParseArtist/mbArtist/mbArtistData in client.go, ArtistTypeFilter
and related filtering functions in api.go, SyncArtistDiscographyWithFilter
in sync.go, and CacheStats/IsArtistCacheValid in cache.go.

Fix bugs: SaveExternalRelease now stores NULL instead of empty string for
zero CachedAt; sync upserts are now transactional with stale release cleanup;
getCachedReleases returns int instead of *CacheStats; doGet uses url.Values
for proper query encoding of MBID.

Fix tests: removed duplicate TestRun_GracefulShutdown, removed dead code
(_ = dbPath) from TestNewApp, fixed assertions in httptest handler goroutine
to avoid data race, increased rate limiter timing tolerance, removed
Client.Close() calls (no-op removed), fixed sync test cache expiry to use
UPDATE instead of 0 TTL races.

Fix formatting: cancel()}() formatting in main.go, error format string in sync.go.

internal/musicbrainz/api.go

@@ -3,6 +3,7 @@ package musicbrainz
 import (
 	"context"
 	"fmt"
+	"net/url"
 	"regexp"
 	"strings"
 	"unicode"
@@ -12,41 +13,17 @@ import (
 
 // excludedStatuses contains release-group statuses that should be filtered out.
 var excludedStatuses = map[string]bool{
-	"Bootleg":          true,
-	"Promotion":        true,
-	"Pseudo-Release":   true,
+	"Bootleg":        true,
+	"Promotion":      true,
+	"Pseudo-Release": true,
 }
 
 // includedTypes contains release-group types that should be included.
 var includedTypes = map[string]bool{
-	"Album":        true,
-	"Single":       true,
-	"EP":           true,
-	"Compilation":  true,
-}
-
-// ArtistTypeFilter holds per-artist type filtering preferences.
-// These are placeholders for Web UI integration where users can
-// toggle which release types to monitor per artist.
-type ArtistTypeFilter struct {
-	// ArtistID is the MusicBrainz artist ID.
-	ArtistID string
-	// IncludeSingles whether to include Single-type release groups.
-	IncludeSingles bool
-	// IncludeCompilations whether to include Compilation-type release groups.
-	IncludeCompilations bool
-	// IncludeEP whether to include EP-type release groups.
-	IncludeEP bool
-}
-
-// DefaultArtistTypeFilter returns an ArtistTypeFilter with all types enabled.
-func DefaultArtistTypeFilter(artistID string) *ArtistTypeFilter {
-	return &ArtistTypeFilter{
-		ArtistID:            artistID,
-		IncludeSingles:      true,
-		IncludeCompilations: true,
-		IncludeEP:           true,
-	}
+	"Album":       true,
+	"Single":      true,
+	"EP":          true,
+	"Compilation": true,
 }
 
 // GetArtistReleaseGroups fetches all release groups for a given artist from MusicBrainz.
@@ -61,7 +38,12 @@ func (c *MusicBrainzClient) GetArtistReleaseGroups(ctx context.Context, artistMB
 	limit := 100 // MusicBrainz max limit per request
 
 	for {
-		path := fmt.Sprintf("/release-group?artist=%s&limit=%d&offset=%d", artistMBID, limit, offset)
+		params := url.Values{}
+		params.Set("artist", artistMBID)
+		params.Set("limit", fmt.Sprintf("%d", limit))
+		params.Set("offset", fmt.Sprintf("%d", offset))
+		path := buildPath("/release-group", params)
+
 		body, err := c.doGet(ctx, path)
 		if err != nil {
 			return nil, fmt.Errorf("fetch release groups for artist %s: %w", artistMBID, err)
@@ -101,22 +83,6 @@ func FilterReleaseGroups(groups []ReleaseGroup) []ReleaseGroup {
 	return filtered
 }
 
-// FilterReleaseGroupsWithArtistFilter applies status filtering, base type filtering,
-// and per-artist type filtering preferences.
-func FilterReleaseGroupsWithArtistFilter(groups []ReleaseGroup, artistFilter *ArtistTypeFilter) []ReleaseGroup {
-	var filtered []ReleaseGroup
-	for _, rg := range groups {
-		if IsStatusExcluded(rg.Status) {
-			continue
-		}
-		if !IsTypeIncludedForArtist(rg.Type, artistFilter) {
-			continue
-		}
-		filtered = append(filtered, rg)
-	}
-	return filtered
-}
-
 // IsStatusExcluded returns true if the given status should be excluded.
 func IsStatusExcluded(status string) bool {
 	return excludedStatuses[status]
@@ -127,34 +93,13 @@ func IsTypeIncluded(releaseType string) bool {
 	return includedTypes[releaseType]
 }
 
-// IsTypeIncludedForArtist checks whether a release type should be included
-// based on per-artist type filtering preferences.
-func IsTypeIncludedForArtist(releaseType string, filter *ArtistTypeFilter) bool {
-	if filter == nil {
-		return IsTypeIncluded(releaseType)
-	}
-
-	switch releaseType {
-	case "Album":
-		return true // Albums are always included
-	case "Single":
-		return filter.IncludeSingles
-	case "EP":
-		return filter.IncludeEP
-	case "Compilation":
-		return filter.IncludeCompilations
-	default:
-		return false
-	}
-}
-
 // NormalizeString normalizes a string for fuzzy matching by:
-// - Converting to lowercase
-// - Removing special characters (keeping only letters, digits, and spaces)
-// - Removing years (4-digit numbers that look like years)
-// - Removing bracketed keywords (e.g., [Deluxe], [Remastered])
-// - Collapsing multiple spaces into one
-// - Trimming leading/trailing whitespace
+//   - Converting to lowercase
+//   - Removing special characters (keeping only letters, digits, and spaces)
+//   - Removing years (4-digit numbers that look like years)
+//   - Removing bracketed keywords (e.g., [Deluxe], [Remastered])
+//   - Collapsing multiple spaces into one
+//   - Trimming leading/trailing whitespace
 func NormalizeString(s string) string {
 	// Convert to lowercase
 	s = strings.ToLower(s)
@@ -212,7 +157,7 @@ func NormalizeArtistName(name string) string {
 }
 
 // ToExternalRelease converts a ReleaseGroup to an ExternalRelease
-// with the current timestamp as CachedAt.
+// for database persistence.
 func (rg *ReleaseGroup) ToExternalRelease() *database.ExternalRelease {
 	return &database.ExternalRelease{
 		RGID:        rg.ID,