feat: Always enable embeddings, remove config toggle

[colbymchenry]

Summary

• Removes the enableEmbeddings config option entirely — embeddings are now always enabled
• Vector manager is created eagerly in the CodeGraph constructor (model download + embedding generation still happen lazily)
• Updates visualizer server to remove the config toggle step from the embeddings generate endpoint

Why

Testing with 13 queries ranging from exact symbol lookups to natural language showed that semantic search consistently outperforms FTS-only search for the kinds of queries Claude writes:

• "ExtractionOrchestrator" — FTS returned rootDir (a property) as How do you use this across multiple projects #1; semantic correctly returned the class
• "how does file parsing work" — FTS returned readJsonFile (config I/O); semantic returned getParser
• "database connection management" — FTS returned optimize; semantic found DatabaseConnection
• "resolves references between modules" — FTS found framework-specific helpers; semantic found the main resolveOne orchestrator

FTS has a ranking problem where properties/methods that match tokens often outrank the conceptually relevant class or function. Semantic search understands intent.

Test plan

• All 21 vector tests pass (updated the one test that expected null stats)
• Build succeeds
• Backward compatible — old config files with enableEmbeddings field are harmlessly ignored during config merge

🤖 Generated with Claude Code