#21498: fix #20898: handle array type in tryFlattenLiteralAnyOf

## Summary `tryFlattenLiteralAnyOf` silently fails when a schema variant uses `type: ["string"]` instead of `type: "string"`, even though both are valid JSON Schema. ## Changes - `src/agents/schema/clean-for-gemini.ts`: Handle array type (e.g., `type: ["string"]`) in addition to string type. ## Testing - [x] Code compiles and passes format check <!-- greptile_comment --> <h3>Greptile Summary</h3> Extended `tryFlattenLiteralAnyOf` to handle array type syntax (e.g., `type: ["string"]`) in addition to string type syntax (e.g., `type: "string"`), both valid per JSON Schema spec. This prevents silent failures when flattening literal anyOf variants. - handled single-element array types in `tryFlattenLiteralAnyOf` logic - aligns with existing `isNullSchema` pattern which already handles array types - missing type validation: array element should be verified as string (see comment) <h3>Confidence Score: 3/5</h3> - This PR is mostly safe but has a minor type safety gap that should be addressed - The change correctly handles array type syntax and aligns with JSON Schema spec and existing patterns in the file (like `isNullSchema`). However, missing type validation for the array element at line 72 creates a potential runtime issue - if `v.type[0]` is not a string, the subsequent type comparison logic could behave unexpectedly. This is a logical error that needs to be fixed. - src/agents/schema/clean-for-gemini.ts requires attention for the type validation issue _{Last reviewed commit: 2e8be7a} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->