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/services/kb/voyage.py

@@ -0,0 +1,55 @@
+"""Voyage embeddings client — voyage-multilingual-2, 1024-dim."""
+
+from __future__ import annotations
+
+import logging
+import os
+from typing import Literal
+
+import httpx
+
+logger = logging.getLogger("shira.kb.voyage")
+
+_VOYAGE_URL = "https://api.voyageai.com/v1/embeddings"
+_MAX_BATCH = 128
+
+
+class VoyageError(RuntimeError):
+    pass
+
+
+async def embed(
+    texts: list[str],
+    input_type: Literal["document", "query"] = "document",
+    model: str | None = None,
+) -> list[list[float]]:
+    if not texts:
+        return []
+
+    api_key = os.environ.get("VOYAGE_API_KEY")
+    if not api_key:
+        raise VoyageError("VOYAGE_API_KEY is not set")
+
+    model = model or os.environ.get("VOYAGE_MODEL", "voyage-multilingual-2")
+
+    out: list[list[float]] = []
+    async with httpx.AsyncClient(timeout=60) as http:
+        for start in range(0, len(texts), _MAX_BATCH):
+            batch = texts[start : start + _MAX_BATCH]
+            resp = await http.post(
+                _VOYAGE_URL,
+                headers={"Authorization": f"Bearer {api_key}"},
+                json={"model": model, "input": batch, "input_type": input_type},
+            )
+            if resp.status_code != 200:
+                raise VoyageError(f"Voyage API {resp.status_code}: {resp.text[:200]}")
+            data = resp.json()
+            for item in sorted(data["data"], key=lambda d: d["index"]):
+                out.append(item["embedding"])
+            logger.info(
+                "[kb.voyage] embedded batch=%d/%d type=%s",
+                min(start + _MAX_BATCH, len(texts)),
+                len(texts),
+                input_type,
+            )
+    return out