feat(phase3): add The Librarian agent with library-desk integration

Library-Desk API Client:
- Async HTTP client with httpx for library-desk API
- HybridRAG search (vector + graph + web)
- Wiki operations (search, get, list, create, update)
- Smart page creation with HybridRAG research
- Semantic vector search and knowledge graph queries
- Dossier browsing and health checks

Librarian Tools (11 total):
- Research: hybrid_search, search_wiki, get_wiki_page, semantic_search
- Browse: list_dossiers, get_dossier_pages, explore_knowledge_graph
- Graph: find_related_entities
- Write: create_wiki_page, update_wiki_page, smart_create_wiki_page

Agent:
- PydanticAI agent with research assistant personality
- System prompt with research and writing workflows
- Streaming support via run_librarian_stream()

Capability:
- LIBRARIAN_CAPABILITY definition for Household Registry
- Automatic registration on startup

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/agents/librarian/__init__.py

@@ -0,0 +1,30 @@
+"""
+The Librarian - Expert agent for research and knowledge management.
+
+Connects to the library-desk API to provide:
+- HybridRAG search (vector + graph + web)
+- Wiki.js operations
+- Knowledge graph queries
+- Semantic search
+"""
+from src.agents.librarian.agent import (
+    get_librarian_agent,
+    run_librarian,
+    run_librarian_stream,
+)
+from src.agents.librarian.capability import (
+    LIBRARIAN_CAPABILITY,
+    get_librarian_capability,
+    register_librarian,
+    unregister_librarian,
+)
+
+__all__ = [
+    "LIBRARIAN_CAPABILITY",
+    "get_librarian_capability",
+    "get_librarian_agent",
+    "register_librarian",
+    "unregister_librarian",
+    "run_librarian",
+    "run_librarian_stream",
+]