fix(dashboard): enrich 400 errors on create to surface plan-limit messages (CLI-1J8)

[BYK]

Summary

• Widen enrichDashboardError to handle 400 on create (not just update), so plan-limit messages like "You may not exceed 10 dashboards on your current plan." surface clearly instead of a raw ApiError: Failed to create dashboard: 400 Bad Request
• Add test for 400 on create with plan-limit detail

Fixes CLI-1J8.

Note: CLI-1JD (explore 400 from open-ended time ranges) was already fixed in #884.

[github-actions]

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Codecov Results 📊

✅ 6378 passed | Total: 6378 | Pass Rate: 100% | Execution Time: 0ms

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +1
Passed Tests	📈 +1
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 83.33%. Project has 13166 uncovered lines.
✅ Project coverage is 75.89%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
src/commands/dashboard/resolve.ts	83.33%	⚠️ 1 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    75.89%    75.89%        —%
==========================================
  Files          294       294         —
  Lines        54604     54606        +2
  Branches         0         0         —
==========================================
+ Hits         41440     41440         —
- Misses       13164     13166        +2
- Partials         0         0         —

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