[Code scan] Tighten Codecov thresholds so coverage checks can fail

[njzjz]

This issue was found by a Codex global code scan of the repository.

Affected code:

dargs/codecov.yml

Lines 3 to 10 in b4db564

	coverage:
	status:
	project:
	default:
	threshold: 100%
	patch:
	default:
	threshold: 100%

Problem:
Both project and patch Codecov statuses set threshold: 100%. In Codecov status configuration, threshold is the allowed coverage drop, not the target coverage. The official docs describe it as allowing coverage to drop by the configured percentage while still posting success: https://docs.codecov.com/docs/commit-status

Observed behavior:
A 100% threshold makes the coverage statuses extremely lenient while appearing strict in the configuration.

Expected behavior:
Use a realistic threshold such as 0% or 1%, and set target separately if the repository wants a specific coverage target.