Add optional per-test descriptions to Emberfall test definitions and CLI output

[talentedmrjones]

Summary

Emberfall test definitions support fields like id, url, method, body, and expect, but there is no optional human-readable per-test description in the documented YAML schema or runtime test struct today (README.md, internal/engine/test.go). CLI reporting currently prints only PASS|FAIL : METHOD URL, which makes repeated or similar tests hard to distinguish during longer runs (internal/engine/test.go); the same friction already shows up in the docs, where the same endpoint is exercised twice for different reasons and the intent lives only in comments (README.md).

Requested change

• Add an optional human-readable description field to each test definition.
• Surface that description in CLI output so repeated or similar tests are easier to interpret.
• Keep the GitHub Action aligned with the same output behavior, since it shells out to the CLI today (action.yml).
• Preserve compatibility for existing test files that do not set the new field.

Acceptance criteria

• A test definition can include an optional human-readable description.
• CLI output clearly distinguishes repeated or similar tests when a description is present.
• Existing configs continue to work unchanged when no description is set.
• Docs and CLI output tests are updated to cover the new behavior (tests/cli.bats).