Fix explorer UI to use tx_count and broaden pytest discovery

- Use tx_count instead of block.transactions.length in latest blocks table
- Fix block modal to show tx_count only and remove misleading transaction list rendering
- Add root-level pytest.ini with broader test paths including apps/*/tests and tests/
- This fixes the block-detail/rendering mismatch where UI expected transactions array but RPC returns tx_count

pytest.ini

@@ -0,0 +1,10 @@
+[pytest]
+testpaths = tests apps/blockchain-node/tests apps/coordinator-api/tests apps/wallet/tests cli/tests
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+addopts = -v --tb=short
+markers =
+    slow: marks tests as slow
+    integration: marks tests as integration tests
+    unit: marks tests as unit tests