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.

src/query/schema.ts

@@ -139,6 +139,7 @@ export function querySchema(
     let result = comparisons.get(key);
     if (!result) {
       const fields: GraphQLInputFieldConfigMap = { eq: { type: value }, isNull: { type: GraphQLBoolean } };
+      if (base.kind === "scalar" && base.name === "string") fields.containsInsensitive = { type: value };
       if (base.kind === "scalar" && base.name !== "bytes")
         fields.in = { type: new GraphQLList(new GraphQLNonNull(value)) };
       if (base.kind === "scalar" && base.name !== "bool" && base.name !== "bytes")