T10: Monitoring, Performance, Documentation & Environment Config — 38 tests, ruff clean, docs OK

- Extended health endpoint: DB+Redis+Storage+Worker checks with degraded status
- Prometheus metrics endpoint: admin-only, text/plain format
- Metrics: http_requests_total, db_pool_connections, arq_jobs_total
- Structured JSON logging (structlog): timestamp, level, method, path, status, duration_ms, tenant_id
- Performance: page_size max 100 enforced (422), streaming CSV export (StreamingResponse)
- Scripts: seed_perf_data.py, check_indexes.py
- Docs: admin-guide.md (Deploy, Backup, Restore, Env-Vars, Troubleshooting), api-overview.md
- README updated: prod setup, API section, env profiles, admin-guide link
- .env.example: added SECRET_KEY, STORAGE_PATH, SMTP_* vars
- 38 new tests, full regression 564/564 pass (0 failures)
- Ruff: all checks passed

app/routes/companies.py

@@ -71,18 +71,66 @@ async def export_companies(
     db: AsyncSession = Depends(get_db),
     current_user: dict = Depends(get_current_user),
 ):
-    """Export companies as CSV or XLSX."""
+    """Export companies as CSV (streaming) or XLSX (buffered)."""
     tenant_id = uuid.UUID(current_user["tenant_id"])
 
     if format == "csv":
-        csv_data = await company_service.export_companies_csv(
-            db,
-            tenant_id,
-            industry=industry,
-            search=search,
-        )
-        return Response(
-            content=csv_data,
+        from app.models.company import Company
+        from sqlalchemy import select as sa_select
+        from app.core.db import get_session_factory
+        import csv
+        import io
+        from fastapi.responses import StreamingResponse
+
+        async def generate_csv():
+            """Async generator yielding CSV rows (streaming, not buffered).
+            Creates its own DB session to avoid request-scoped session issues.
+            """
+            output = io.StringIO()
+            writer = csv.writer(output)
+            header = [
+                "id", "name", "account_number", "industry", "phone",
+                "email", "website", "description", "created_at", "updated_at",
+            ]
+            writer.writerow(header)
+            yield output.getvalue()
+            output.seek(0)
+            output.truncate(0)
+
+            batch_size = 500
+            offset = 0
+            factory = get_session_factory()
+            async with factory() as session:
+                while True:
+                    q = sa_select(Company).where(
+                        Company.tenant_id == tenant_id,
+                        Company.deleted_at.is_(None),
+                    )
+                    if industry:
+                        q = q.where(Company.industry == industry)
+                    if search:
+                        pattern = f"%{search}%"
+                        q = q.where(Company.name.ilike(pattern))
+                    q = q.order_by(Company.name.asc()).offset(offset).limit(batch_size)
+                    result = await session.execute(q)
+                    companies = result.scalars().all()
+                    if not companies:
+                        break
+                    for c in companies:
+                        writer.writerow([
+                            str(c.id), c.name, c.account_number or "", c.industry or "",
+                            c.phone or "", c.email or "", c.website or "",
+                            c.description or "",
+                            c.created_at.isoformat() if c.created_at else "",
+                            c.updated_at.isoformat() if c.updated_at else "",
+                        ])
+                    yield output.getvalue()
+                    output.seek(0)
+                    output.truncate(0)
+                    offset += batch_size
+
+        return StreamingResponse(
+            generate_csv(),
             media_type="text/csv",
             headers={"Content-Disposition": "attachment; filename=companies.csv"},
         )