feat: add comments and cleanup unused imports across codebase

internal/db/helpers.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 )
 
+// NullStringOr returns n.String if valid and non-empty, otherwise fallback
 func NullStringOr(n sql.NullString, fallback string) string {
 	if n.Valid && n.String != "" {
 		return n.String
@@ -14,6 +15,7 @@ func NullStringOr(n sql.NullString, fallback string) string {
 	return fallback
 }
 
+// DisplayTitle returns the English title, falling back to Japanese then original
 func DisplayTitle(titleEnglish, titleJapanese sql.NullString, titleOriginal string) string {
 	return NullStringOr(titleEnglish, NullStringOr(titleJapanese, titleOriginal))
 }
@@ -22,6 +24,7 @@ func (r GetUserWatchListRow) DisplayTitle() string {
 	return DisplayTitle(r.TitleEnglish, r.TitleJapanese, r.TitleOriginal)
 }
 
+// BoolPtr converts a nullable bool to a pointer; nil if not valid
 func BoolPtr(b sql.NullBool) *bool {
 	if !b.Valid {
 		return nil
@@ -29,6 +32,7 @@ func BoolPtr(b sql.NullBool) *bool {
 	return &b.Bool
 }
 
+// BeginTx starts a transaction and returns the Queries wrapper bound to it
 func BeginTx(ctx context.Context, db *sql.DB) (*Queries, *sql.Tx, error) {
 	if db == nil {
 		return nil, nil, errors.New("database unavailable")