Show verification service errors

[madebygps]

Summary

• show a visible retryable error when a Durable verification job fails, is canceled, or is terminated
• keep deleting failed active jobs so learners can retry without the attempt counting
• add route coverage for the failed Durable status UI path

Validation

• cd api && uv run ruff check . ../packages/learn-to-cloud-shared
• cd api && uv run ruff format --check . ../packages/learn-to-cloud-shared
• cd api && uv run ty check --exclude scripts --exclude tests .
• cd packages/learn-to-cloud-shared && uv run ty check --exclude tests .
• cd apps/verification-functions && uv run ruff check . && uv run ruff format --check . && uv run ty check . && uv run python -c "import function_app"
• cd api && uv run pytest tests/ -x
• cd packages/learn-to-cloud-shared && uv run pytest tests/ -x
• API smoke checks for /health, /ready, and /openapi.json