Remove LLM, Storpheus, HuggingFace, and Qdrant from codebase

All of these were mono-repo leftovers from when MuseHub co-existed with an AI music generation service. MuseHub is now a standalone VCS platform with no LLM, vector DB, or neural MIDI generation dependencies.

Removed: - config.py: ALLOWED_MODEL_IDS, APPROVED_MODELS, CONTEXT_WINDOW_TOKENS, get_context_window_tokens, DEFAULT_TEMPO, llm_*, openrouter_api_key, qdrant_*, storpheus_* (12 settings), hf_api_key, hf_timeout, skip_expressiveness, max_concurrent_compositions_per_user, orchestration_*/composition_*/agent_reasoning_* settings, section/instrument/bass agent watchdog timeouts - musehub_qdrant.py: entire Qdrant vector DB service - musehub_embeddings.py: entire musical feature embedding service - search.py: /search/similar endpoint (Qdrant-backed semantic search) - musehub_sync.py: embed_push_commits background task and its imports - models/musehub.py: SimilarCommitResponse, SimilarSearchResponse - contracts/json_types.py: StorpheusResultBucket - tests/test_musehub_embeddings.py: deleted - tests/test_musehub_search.py: removed all similarity search tests - tests/conftest.py: removed _disable_storpheus_hard_gate fixture - docker-compose.yml: removed qdrant service and qdrant_data volume - requirements.txt + pyproject.toml: removed qdrant-client, openai, gradio-client, beautifulsoup4, lxml - .env.example: removed OPENROUTER_API_KEY and HF_API_KEY sections