feat: Switch to persistent Chroma HTTP server

Replace MCP subprocess approach with persistent Chroma HTTP server for
improved performance and reliability. This re-enables Chroma on Windows
by eliminating the subprocess spawning that caused console popups.

Changes:
- NEW: ChromaServerManager.ts - Manages local Chroma server lifecycle
  via `npx chroma run`
- REFACTOR: ChromaSync.ts - Uses chromadb npm package's ChromaClient
  instead of MCP subprocess (removes Windows disabling)
- UPDATE: worker-service.ts - Starts Chroma server on initialization
- UPDATE: GracefulShutdown.ts - Stops Chroma server on shutdown
- UPDATE: SettingsDefaultsManager.ts - New Chroma configuration options
- UPDATE: build-hooks.js - Mark optional chromadb deps as external

Benefits:
- Eliminates subprocess spawn latency on first query
- Single server process instead of per-operation subprocesses
- No Python/uvx dependency for local mode
- Re-enables Chroma vector search on Windows
- Future-ready for cloud-hosted Chroma (claude-mem pro)
- Cross-platform: Linux, macOS, Windows

Configuration:
  CLAUDE_MEM_CHROMA_MODE=local|remote
  CLAUDE_MEM_CHROMA_HOST=127.0.0.1
  CLAUDE_MEM_CHROMA_PORT=8000
  CLAUDE_MEM_CHROMA_SSL=false

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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