Fix/route error digest

[Devadakene]

Closes #130

Description

This PR resolves the issue where server-side error digests were discarded by the shared RouteError fallback component. Now, when error.digest is present, it is rendered in a small, clearly-labeled, and low-emphasis format beneath the error message to facilitate easier tracing of production logs.

Changes

Components

• Modified RouteError.tsx to conditionally render the error digest underneath the existing error message paragraph when error.digest is present.

Tests

• Modified RouteError.test.tsx to add:
  • A test case verifying the digest is correctly rendered in the fallback UI when error.digest is present.
  • A test case verifying that no reference line or digest block is rendered when error.digest is undefined.

Verification

• Checked test runner and verified all 10 tests passed successfully.
• Validated that the repository standard of >95% test coverage remains fully satisfied.