feat(kb): Phase 1 — Israeli National Insurance knowledge base

Adds a searchable KB for חוק הביטוח הלאומי, תקנות הביטוח הלאומי, and חוזרי
הביטוח הלאומי. Hybrid search (pgvector cosine + tsvector/trgm) fused with
Reciprocal Rank Fusion, exposed to Shira as the `search_insurance_kb` tool.

- api/services/kb/: asyncpg pool, Voyage voyage-multilingual-2 client,
  per-kind chunker (statute-by-section / circular header-aware), ingest
  pipeline with supersession (old source → superseded_by), hybrid search.
- api/routes/admin_kb.py: POST /admin/kb/ingest (multipart), GET /admin/kb/stats.
- mcp_server/tools/legal_kb_tools.py: `search_insurance_kb` registered under
  the `legal` toolset.
- pyproject.toml: +asyncpg, +python-docx, +boto3, +python-multipart.

Infra (external): pgvector/pgvector:pg16 on the shared PG, insurance_kb DB
with hnsw + gin indexes, MinIO bucket insurance-kb, KB_DATABASE_URL in
Infisical /espocrm, VOYAGE_API_KEY/VOYAGE_MODEL/KB_DATABASE_URL on the
shira-hermes Coolify app.

Refs Task Master #2

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/main.py

@@ -9,6 +9,7 @@ from pathlib import Path
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
+from api.routes.admin_kb import router as admin_kb_router
 from api.routes.health import router as health_router
 from api.routes.smart_assistant import router as smart_assistant_router
 
@@ -34,6 +35,7 @@ app.add_middleware(
 
 app.include_router(health_router)
 app.include_router(smart_assistant_router)
+app.include_router(admin_kb_router)
 
 
 @app.on_event("startup")