Add native literal substring query predicates

Implement checked containsInsensitive string predicates in GraphQL, protobuf,
native SQL and bounded residual evaluation. ASCII folding is deterministic;
SQL pattern characters remain literal. Retain deferred full-text index design.

Studio migration awaits a decision on checked native getter forwarding across
conformances; do not duplicate titles or bypass private state ownership.
Compiler and local full-stack substring-query acceptance pass.

proto/camino/schema.proto

@@ -165,6 +165,7 @@ enum QueryComparisonOperator {
   QUERY_COMPARISON_OPERATOR_LTE = 5;
   QUERY_COMPARISON_OPERATOR_GT = 6;
   QUERY_COMPARISON_OPERATOR_GTE = 7;
+  QUERY_COMPARISON_OPERATOR_CONTAINS_INSENSITIVE = 8;
 }
 message QueryComparison {
   QueryOperand operand = 1;