fix(11-05): sync single-statement and plain-transaction writes, type engine status errors

- pin the sync callbacks before gorm:commit_or_rollback_transaction: an
  After-only anchor is appended past the commit and lagoon's after-commit
  flush, so single-statement writes never synced
- give the gate and the document builder a clean session: Session with NewDB
  and a Context clones the write's statement, and a later WithContext queried
  through the written model's table
- typesense.StatusError carries method, path and status, never the body
- README: sync semantics, the three gates, delete on soft delete, and the
  SQL re-gate required of SearchIDs callers

modules/beachcomber/typesense/engine.go

@@ -317,6 +317,21 @@ func unwrapURLError(err error) error {
 
 func ok2xx(code int) bool { return code >= 200 && code < 300 }
 
-func statusError(method, path string, code int) error {
-	return fmt.Errorf("typesense: %s %s: status %d", method, path, code)
+// StatusError is a Typesense answer outside 2xx. It carries the method,
+// path and status, never the answer body, which could echo request data.
+type StatusError struct {
+	Method string
+	Path   string
+	Code   int
+}
+
+func (e *StatusError) Error() string {
+	return fmt.Sprintf("typesense: %s %s: status %d", e.Method, e.Path, e.Code)
+}
+
+// StatusCode returns the HTTP status Typesense answered with.
+func (e *StatusError) StatusCode() int { return e.Code }
+
+func statusError(method, path string, code int) error {
+	return &StatusError{Method: method, Path: path, Code: code}
 }