Add CSV export of scan results

The Review tab gets an Export CSV menu: "This view" exports the current
status filter and search, "Entire scan" exports every scanned slave file.

Each row carries status, match type, a recommendation, slave/master paths,
the link target, the match reason, sizes, codec details for both sides,
the quality verdict, notes, errors and timestamps. Rows are streamed in
pages of 1000 so a large export never holds the database connection a
running scan needs. The file starts with a UTF-8 BOM for Excel, and cells
a spreadsheet would evaluate as formulas are prefixed with an apostrophe.

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

internal/store/models.go

@@ -314,7 +314,8 @@ type MatchFilter struct {
 	Offset int
 }
 
-func (s *Store) Matches(ctx context.Context, pairID int64, f MatchFilter) ([]Match, int, error) {
+// matchWhere builds the WHERE clause shared by listing and export.
+func matchWhere(pairID int64, f MatchFilter) (string, []any) {
 	where := []string{"pair_id = ?"}
 	args := []any{pairID}
 	switch f.Status {
@@ -334,7 +335,11 @@ func (s *Store) Matches(ctx context.Context, pairID int64, f MatchFilter) ([]Mat
 		q := "%" + strings.NewReplacer(`\`, `\\`, `%`, `\%`, `_`, `\_`).Replace(f.Query) + "%"
 		args = append(args, q, q)
 	}
-	w := strings.Join(where, " AND ")
+	return strings.Join(where, " AND "), args
+}
+
+func (s *Store) Matches(ctx context.Context, pairID int64, f MatchFilter) ([]Match, int, error) {
+	w, args := matchWhere(pairID, f)
 	var total int
 	if err := s.DB.QueryRowContext(ctx, `SELECT COUNT(*) FROM matches WHERE `+w, args...).Scan(&total); err != nil {
 		return nil, 0, err
@@ -359,6 +364,45 @@ func (s *Store) Matches(ctx context.Context, pairID int64, f MatchFilter) ([]Mat
 	return out, total, rows.Err()
 }
 
+// ExportMatches calls fn for every match of the filter, ordered by slave
+// path. Rows are read in pages so a slow download never holds the database
+// connection (scans need it) for longer than one page.
+func (s *Store) ExportMatches(ctx context.Context, pairID int64, f MatchFilter, fn func(Match) error) error {
+	const page = 1000
+	w, args := matchWhere(pairID, f)
+	after := ""
+	for {
+		rows, err := s.DB.QueryContext(ctx, `SELECT `+matchCols+` FROM matches WHERE `+w+
+			` AND rel_slave > ? ORDER BY rel_slave LIMIT ?`, append(append([]any{}, args...), after, page)...)
+		if err != nil {
+			return err
+		}
+		batch := make([]Match, 0, page)
+		for rows.Next() {
+			m, err := scanMatch(rows)
+			if err != nil {
+				rows.Close()
+				return err
+			}
+			batch = append(batch, m)
+		}
+		err = rows.Err()
+		rows.Close()
+		if err != nil {
+			return err
+		}
+		for _, m := range batch {
+			if err := fn(m); err != nil {
+				return err
+			}
+		}
+		if len(batch) < page {
+			return nil
+		}
+		after = batch[len(batch)-1].RelSlave
+	}
+}
+
 // IdenticalIDs lists linkable identical matches (not ignored).
 func (s *Store) IdenticalIDs(ctx context.Context, pairID int64) ([]int64, error) {
 	rows, err := s.DB.QueryContext(ctx, `SELECT id FROM matches WHERE pair_id = ? AND status = 'identical' AND ignored = 0 ORDER BY rel_slave`, pairID)