fix: add required search_mode param to knowledge_hit_test

[itsablabla]

Summary

MaxKB API requires the search_mode field in hit_test requests. Without it, the API returns a 500 error (搜索模式:该字段不能为 null). This adds the search_mode parameter to the knowledge_hit_test tool with three options:

• embedding (vector search) — default
• keywords (full-text search)
• blend (hybrid)

Discovered during a routine health check of maxkb.garzaos.cloud — all 3 knowledge bases are healthy and retrieval works correctly with this fix applied.

Review & Testing Checklist for Human

• Verify knowledge_hit_test works via the MCP server with each search mode (embedding, keywords, blend)
• Confirm the default embedding mode returns results without requiring the caller to specify it

Notes

• Also restarted both MaxKB containers on VPS (they were down with exit code 255) and fixed restart policies to unless-stopped
• The MaxKB MCP container on VPS at /docker/maxkb-mcp needs to be rebuilt with docker compose up -d --build to pick up this fix
• VPS health: 73% disk, 10/31 GB RAM, all 3 KBs operational (147 total documents, 2.9M+ chars)

Link to Devin session: https://app.devin.ai/sessions/80ece13d93aa4fcfb3d108cba74953ff
Requested by: @itsablabla

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