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/src/app/models/__init__.py

@@ -52,6 +52,7 @@ from ..schemas import (
 from ..domain import (
     Job,
     Miner,
+    JobReceipt,
     MarketplaceOffer,
     MarketplaceBid,
     User,
@@ -93,6 +94,7 @@ __all__ = [
     "Constraints",
     "Job",
     "Miner",
+    "JobReceipt",
     "MarketplaceOffer",
     "MarketplaceBid",
     "ServiceType",