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>

pyproject.toml

@@ -11,6 +11,10 @@ dependencies = [
     "openai>=1.50.0",
     "pyyaml>=6.0",
     "pymupdf>=1.24.0",
+    "asyncpg>=0.30.0",
+    "python-docx>=1.1.2",
+    "boto3>=1.35.0",
+    "python-multipart>=0.0.9",
 ]
 
 [project.optional-dependencies]