feat: add transaction hash search to blockchain explorer and cleanup settlement storage

Blockchain Explorer:
- Add transaction hash search support (64-char hex pattern validation)
- Fetch and display transaction details in modal (hash, type, from/to, amount, fee, block)
- Fix regex escape sequence in block height validation
- Update search placeholder text to mention both search types
- Add blank lines between function definitions for PEP 8 compliance

Settlement Storage:
- Add timedelta import for future

apps/coordinator-api/tests/conftest.py

@@ -1,6 +1,8 @@
 """Ensure coordinator-api src is on sys.path for all tests in this directory."""
 
 import sys
+import os
+import tempfile
 from pathlib import Path
 
 _src = str(Path(__file__).resolve().parent.parent / "src")
@@ -15,3 +17,9 @@ if _app_mod and hasattr(_app_mod, "__file__") and _app_mod.__file__ and _src not
 
 if _src not in sys.path:
     sys.path.insert(0, _src)
+
+# Set up test environment
+os.environ["TEST_MODE"] = "true"
+project_root = Path(__file__).resolve().parent.parent.parent
+os.environ["AUDIT_LOG_DIR"] = str(project_root / "logs" / "audit")
+os.environ["TEST_DATABASE_URL"] = "sqlite:///:memory:"