feat: add search_entity_labels tool for fuzzy entity search

[magnus919]

Summary

• Adds search_entity_labels MCP tool wrapping /graph/label/search
• Accepts a list of queries so agents can batch-check multiple entities in one call instead of N round trips
• Returns fuzzy-matched entity names per query; empty list when no match
• Validated against a live instance with 32,000+ entities

Interface

search_entity_labels(queries: ["Brynjolfsson", "Generative AI"], limit: 5)

{
  "results": [
    {"query": "Brynjolfsson", "matches": ["Brynjolfsson", "Brynjolfsson And Mitchell", ...]},
    {"query": "Generative AI", "matches": ["Generative AI", "Generative Ai", ...]}
  ]
}

Note on degree

The /graph/label/search endpoint returns entity names only — degree is not part of the response. The min_degree filter proposed in the issue cannot be implemented without additional per-entity lookups, which would be expensive at scale. Entity names alone are sufficient for the primary use cases (pre-query confirmation, post-insert verification, canonical name lookup).

Closes #5

Test plan

• Call with a single query string and confirm matches returned
• Call with multiple queries and confirm one result entry per query
• Call with a query that matches nothing and confirm matches: []
• Call with limit and confirm result count is capped

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