fix(mcp): return controlled errors for Milvus search failures

[sanjayy0612]

Fixes #251

Problem

The shared MCP search helper handled failures while loading a Milvus collection and generating an embedding, but exceptions from the actual vector search escaped the tool boundary. A transient Milvus timeout could therefore abort documentation, GitHub issue, and code search invocations.

Root cause

_search_collection() called client.search() outside the existing RuntimeError normalization used by the public MCP tools.

Solution

Wrap the Milvus search operation and raise a contextual RuntimeError. Existing tool handlers now return a controlled Search failed: ... response. A regression test simulates a Milvus timeout and verifies that behavior.

Testing

• pytest tests/test_mcp_server.py: 64 passed
• pytest: 168 passed, 6 skipped
• ruff check docs-agent-mcp/mcp-server tests
• ruff format --check docs-agent-mcp/mcp-server tests
• Python compile check
• git diff --check

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