fix(08-09): match wristband OAuth byte contract to live-recorded PHP

Recording the full mcp-lifecycle fixture against real isolated PHP
(08-09-PLAN.md Task 2) uncovered three byte-level gaps between wristband's
assumed contract and actual production PHP behavior:

- Every explicit "Cache-Control: no-store" PHP sets is actually delivered
  as "no-store, private" (Laravel's session-cookie default merges "private"
  onto any explicit value); wristband's own default for unheadered JSON
  error responses is "no-cache, private" (matching the house convention
  already used elsewhere), not empty.
- PHP's redirect responses (authorize success and every error redirect)
  render Symfony's default HTML redirect body with Content-Type
  "text/html; charset=utf-8"; Go's bare 302 with no body never matched.
  wristband/redirect_html.go ports that exact byte template, including
  PHP's htmlspecialchars(ENT_QUOTES) escaping (Go's html.EscapeString uses
  different quote entities).

tide/normalize.go: isIDKey now also masks "_ids" plural array fields
(e.g. collection_ids), a latent parity-corpus gap no prior fixture had
exercised with a literal, non-empty, non-placeholder array value.

tide/normalize.go

@@ -117,7 +117,14 @@ func isIDKey(key string) bool {
 	if key == "id" {
 		return true
 	}
-	return strings.HasSuffix(key, "_id") && !strings.HasSuffix(key, "_at")
+	if strings.HasSuffix(key, "_at") {
+		return false
+	}
+	// "_ids" covers plural raw-integer-array fields such as collection_ids:
+	// each array element still reaches maskLeaf individually (maskValue
+	// recurses into []any before calling maskLeaf), so this masks every
+	// element the same way a singular "_id" scalar would be masked.
+	return strings.HasSuffix(key, "_id") || strings.HasSuffix(key, "_ids")
 }
 
 func lastPathKey(path string) string {