Add bug 47: Fix Collect Coverage button error

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.story_kit/stories/upcoming/47_fix_collect_coverage_button_error.md

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+---
+name: Fix Collect Coverage Button Error
+test_plan: pending
+---
+
+# Bug 47: Fix Collect Coverage Button Error
+
+## Description
+
+Pressing "Collect Coverage" in the workflow gates UI produces a large error. The feature expects a vitest `coverage-summary.json` but the project doesn't have coverage tooling configured.
+
+## Expected Behavior
+
+Either the coverage collection works end-to-end, or the button is hidden/disabled when coverage tooling is not available.
+
+## Steps to Reproduce
+
+1. Start the server
+2. Open the frontend
+3. Navigate to workflow gates
+4. Press "Collect Coverage"
+5. Large error is displayed
+
+## Acceptance Criteria
+
+- [ ] "Collect Coverage" either works or fails gracefully with a clear message
+- [ ] No giant error dump shown to the user