docs: add comprehensive v3+ to v5.0.0 migration guide

- Add detailed migration guide covering all API changes from v3+ to v5.0.0 - Include configuration and authentication changes - Provide before/after examples for all API methods in order: - Auth V1, Listen V1, Speak V1, Agent V1, Read V1, Models V1, Manage V1, Self-Hosted V1 - Integrate WebSocket examples inline with corresponding REST endpoints - Document response type differences (synchronous vs asynchronous with callbacks) - Use consistent UUID4 format for all example IDs - Add migration checklist and breaking changes summary

Author: lukeocodes