Add eBay Browse API integration with daily call quota

eBay marketplaces are now polled through eBay's official Buy > Browse API (client-credentials OAuth2) instead of an Apify scraper actor; Apify still handles Yahoo JP and Mercari. Browse API calls are tracked per day in a new ebay_api_usage table and capped (default 5000, configurable) on eBay's Pacific-time reset clock, so polling halts before the limit is hit. Credentials live in config.toml [ebay] and are overridable via /settings, which also surfaces the day's running call count.

Also carries the server.secure_cookies config plumbing (field, accessor, example) consumed by the following commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/db/queries.go

@@ -213,6 +213,60 @@ func (s *Store) SetSetting(ctx context.Context, key, value string) error {
 	return err
 }
 
+// ============ ebay api usage ============
+
+// ebayResetLoc is the timezone eBay's API rate limits reset in: midnight
+// Pacific (it observes US DST). If the zone database is somehow unavailable
+// we fall back to UTC rather than failing — main.go embeds time/tzdata so in
+// practice the lookup always succeeds.
+var ebayResetLoc = func() *time.Location {
+	loc, err := time.LoadLocation("America/Los_Angeles")
+	if err != nil {
+		return time.UTC
+	}
+	return loc
+}()
+
+// ebayUsageDay returns the date key used to bucket eBay API calls, aligned to
+// eBay's own quota reset (midnight US Pacific).
+func ebayUsageDay() string {
+	return time.Now().In(ebayResetLoc).Format("2006-01-02")
+}
+
+// EbayUsageToday returns the number of eBay Browse API calls recorded for the
+// current UTC day. A missing row counts as zero.
+func (s *Store) EbayUsageToday(ctx context.Context) (int, error) {
+	var n int
+	err := s.DB.QueryRowContext(ctx,
+		`SELECT call_count FROM ebay_api_usage WHERE usage_date = ?`, ebayUsageDay()).Scan(&n)
+	if errors.Is(err, sql.ErrNoRows) {
+		return 0, nil
+	}
+	if err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
+// IncrementEbayUsage records one eBay Browse API call against the current UTC
+// day and returns the new running total.
+func (s *Store) IncrementEbayUsage(ctx context.Context) (int, error) {
+	day := ebayUsageDay()
+	_, err := s.DB.ExecContext(ctx, `
+		INSERT INTO ebay_api_usage (usage_date, call_count) VALUES (?, 1)
+		ON CONFLICT(usage_date) DO UPDATE SET call_count = call_count + 1
+	`, day)
+	if err != nil {
+		return 0, err
+	}
+	var n int
+	if err := s.DB.QueryRowContext(ctx,
+		`SELECT call_count FROM ebay_api_usage WHERE usage_date = ?`, day).Scan(&n); err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
 // ============ items ============
 
 func (s *Store) CreateItem(ctx context.Context, it *models.Item) (int64, error) {