fix(kb): persist vlm_config on knowledge base update

[lyra-planet]

Description

Fixes the knowledge base update API so top-level vlm_config is accepted and persisted by PUT /api/v1/knowledge-bases/{id}.

Previously, UpdateKnowledgeBaseRequest did not expose vlm_config, so Gin ignored the field during JSON binding and the service update path never saw it. The frontend already sends vlm_config when editing a knowledge base, but the backend response and follow-up GET kept the old disabled VLM configuration.

This PR adds vlm_config to the update request DTO, passes it through the knowledge base service update path, persists it only when explicitly provided, and keeps omitted vlm_config requests preserving the existing KB configuration. It also syncs the Go client request type, frontend API typing, and API docs.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📚 Documentation update
• 🎨 Refactor
• ⚡ Performance improvement
• 🧪 Test
• 🔧 Configuration / Build / CI

Related Issue

Fixes #1723

Testing

• gofmt on changed Go files
• go test ./internal/handler ./internal/application/service ./internal/agent/tools
• (cd client && go test ./...)
• Regression coverage added for the issue path:
  • UpdateKnowledgeBaseRequest now binds a top-level vlm_config field from the update JSON body.
  • UpdateKnowledgeBase preserves the existing VLM config when vlm_config is omitted.
  • UpdateKnowledgeBase overwrites the stored VLM config when vlm_config is provided.
• Verified the [Bug]: KB更新API无法设置vlm_config — UpdateKnowledgeBaseRequest缺少VLMConfig字段 #1723 API scenario against a local WeKnora Lite instance:
  • Created a temporary knowledge base with VLM disabled.
  • Sent PUT /api/v1/knowledge-bases/{kbId} with {"name":"test","vlm_config":{"enabled":true,"model_id":"<vlm-model-id>"}}.
  • Confirmed the PUT response and follow-up GET /api/v1/knowledge-bases/{kbId} both returned vlm_config.enabled=true with the same model_id.

Checklist

• Self-reviewed the code
• Added/updated tests covering the change
• Updated related documentation

Screenshots / Recordings

N/A; backend API fix with no UI-visible layout change.