* fix(js-sdk): add Zod v4 compatibility for schema conversion

Replace direct usage of deprecated `zod-to-json-schema` package with a
new utility that supports both Zod v3 and v4. The `zod-to-json-schema`
package is incompatible with Zod v4, causing schema conversion failures
for users who have upgraded to Zod v4.

Changes:
- Create zodSchemaToJson.ts utility with Zod v3/v4 detection
- Add isZodSchema() function to detect Zod schemas
- Add safeZodSchemaToJsonSchema() for graceful conversion
- Update validation.ts, extract.ts, agent.ts, and v1/index.ts
- Add comprehensive unit tests for the new utility

The utility:
- Detects Zod v4 schemas by checking for _zod property
- Falls back to zod-to-json-schema for Zod v3 schemas
- Provides safeZodSchemaToJsonSchema for graceful fallback

Co-Authored-By: rafaelsideguide <rafael@sideguide.dev>

* refactor(js-sdk): simplify zodSchemaToJson utility and tests

- Rename safeZodSchemaToJsonSchema to zodSchemaToJsonSchema (redundant prefix)
- Remove unnecessary comments explaining obvious behavior
- Condense 47 unit tests into 5 comprehensive tests
- Clean up redundant code

Co-Authored-By: rafaelsideguide <rafael@sideguide.dev>

* mv test to right spot

* bump version

---------

Co-authored-by: firecrawl-spring[bot] <254786068+firecrawl-spring[bot]@users.noreply.github.com>
Co-authored-by: rafaelsideguide <rafael@sideguide.dev>
Co-authored-by: rafaelmmiller <150964962+rafaelsideguide@users.noreply.github.com>