feat(knowledge): add LLM wiki knowledge management

[zhagtao]

Summary

• Add LLM wiki ingestion, planning, building, search, evidence, and usage tracking
• Add MySQL persistence, migrations, file storage, indexing, and hybrid search integration
• Expose knowledge wiki APIs and integrate them with chat runtime knowledge queries
• Add LLM wiki management UI for jobs, tree navigation, and document viewing
• Document the architecture and implementation through ADR, HLD, and RFC updates

Testing

• Added comprehensive Go unit and integration tests for ingestion, corpus management, planning, building, evidence, storage, indexing, search, API handlers, and usage tracking
• Added frontend tests for the LLM wiki tree and Knowledge page
• Added coverage for document extraction, LLM client behavior, chat runtime integration, and configuration changes

Author confirmation

• I have read and agree to the project contribution guide. Guide: https://github.com/ongridio/ongrid/blob/main/CONTRIBUTING.md