Add comprehensive tests for all geo GraphQL endpoints

Created test suite covering all 8 main geo service endpoints:
- Basic: products, nodes (with filters/bounds), clusteredNodes
- Nearest: nearestHubs, nearestOffers, nearestSuppliers (with product filters)
- Routing: routeToCoordinate, autoRoute, railRoute
- Edge cases: invalid coordinates, zero radius, nonexistent UUIDs

Test suite uses real API calls to production GraphQL endpoint.
16 tests total across 4 test classes.

Files:
- tests/test_graphql_endpoints.py: Main test suite (600+ lines)
- tests/README.md: Documentation and usage guide
- pytest.ini: Pytest configuration
- run_tests.sh: Convenience script to run tests
- pyproject.toml: Added pytest and requests as dev dependencies

tests/README.md

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+# Geo Service Tests
+
+Comprehensive test suite for all GraphQL endpoints in the geo service.
+
+## Test Coverage
+
+### Basic Endpoints (4 tests)
+- `test_products_query` - List all unique products
+- `test_nodes_query_basic` - List hubs/nodes without filters
+- `test_nodes_query_with_filters` - Filter nodes by transport type and country
+- `test_nodes_query_with_bounds` - Filter nodes by geographic bounds
+- `test_clustered_nodes_query` - Map clustering for visualization
+
+### Nearest Endpoints (6 tests)
+- `test_nearest_hubs` - Find hubs near coordinates
+- `test_nearest_hubs_with_product_filter` - Find hubs with specific product
+- `test_nearest_offers` - Find offers near coordinates
+- `test_nearest_offers_with_product_filter` - Find offers for specific product
+- `test_nearest_suppliers` - Find suppliers near coordinates
+- `test_nearest_suppliers_with_product_filter` - Find suppliers with product
+
+### Routing Endpoints (3 tests)
+- `test_route_to_coordinate` - Multi-hop route from offer to destination
+- `test_auto_route` - Road route between coordinates (requires OSRM)
+- `test_rail_route` - Rail route between coordinates
+
+### Edge Cases (3 tests)
+- `test_nearest_with_zero_radius` - Very small search radius
+- `test_invalid_coordinates` - Invalid lat/lon values
+- `test_nonexistent_uuid` - Non-existent offer UUID
+
+**Total: 16 tests covering 8 main endpoints**
+
+## Running Tests
+
+### Local Testing (against production)
+
+```bash
+cd backends/geo
+poetry install
+poetry run pytest tests/test_graphql_endpoints.py -v
+```
+
+### Testing against different endpoint
+
+```bash
+export TEST_GEO_URL=https://geo-staging.example.com/graphql/public/
+poetry run pytest tests/test_graphql_endpoints.py -v
+```
+
+### Run specific test class
+
+```bash
+poetry run pytest tests/test_graphql_endpoints.py::TestNearestEndpoints -v
+```
+
+### Run single test
+
+```bash
+poetry run pytest tests/test_graphql_endpoints.py::TestNearestEndpoints::test_nearest_offers -v
+```
+
+### Show print output
+
+```bash
+poetry run pytest tests/test_graphql_endpoints.py -v -s
+```
+
+## CI Integration
+
+Tests should be run on each deployment:
+
+```yaml
+# .gitea/workflows/test.yml
+- name: Run geo endpoint tests
+  run: |
+    cd backends/geo
+    poetry install
+    export TEST_GEO_URL=https://geo.optovia.ru/graphql/public/
+    poetry run pytest tests/test_graphql_endpoints.py -v
+```
+
+## Test Data Requirements
+
+Tests use real data from the production/staging database. Required data:
+- At least one product in `products` collection
+- At least one hub node with coordinates
+- At least one offer with coordinates
+- Graph edges for routing tests
+
+## Expected Test Results
+
+All tests should pass on production environment. Some tests may be skipped if:
+- No products exist: `test_nearest_hubs_with_product_filter`, `test_nearest_offers_with_product_filter`
+- No offers exist: `test_route_to_coordinate`
+- OSRM not configured: `test_auto_route`, `test_rail_route` (warnings, not failures)
+
+## Troubleshooting
+
+### All nearest* tests return 0 results
+
+Check that nodes collection has documents with:
+- Valid `latitude` and `longitude` fields (not null)
+- Correct `node_type` field (`'hub'`, `'offer'`, `'supplier'`)
+
+Query ArangoDB directly:
+
+```javascript
+// Count offers with coordinates
+db._query(`
+  FOR node IN nodes
+    FILTER node.node_type == 'offer'
+    FILTER node.latitude != null AND node.longitude != null
+    RETURN node
+`).toArray().length
+```
+
+### Test failures with 400 errors
+
+Check GraphQL schema matches test queries. GraphQL validation errors indicate:
+- Missing required arguments
+- Wrong argument types
+- Invalid field names
+
+### Connection errors
+
+Verify:
+- TEST_GEO_URL points to correct endpoint
+- Endpoint is accessible (not behind VPN/firewall)
+- GraphQL endpoint is `/graphql/public/` not `/graphql/`