fix(plans): plan list ramp label ignores percent/interval and disagrees with Edit #1185

Summary

The plans list and plan details label a stored ramp from its type alone, which can disagree with Edit (#1183) and with the real interval.

Evidence (origin/main with #1183)

formatBackendRampSchedule (frontend/src/plans.ts:1061-1069) keys only on type:

• A stored weekly 20%/7d plan shows "Weekly 20%" in the list, while Edit opens it as Custom 20% / 7 days.
• A stored weekly 25%/14d plan shows "Weekly 25%" in the list, which hides the 14-day interval, while Edit opens it as Custom 25% / 14 days.

Related cosmetic gap: generatePlanName (plans.ts:1882) uses Math.ceil for "(N steps)", while the backend and the preview floor. A 30% plan gets a name saying "(4 steps)" for a 3-step schedule.

Proposed fix

Derive the list label from the same preset-equality rule Edit uses: a preset name only when type, percent and interval match, otherwise "Custom N% every D days". Use the same step count as the backend in generatePlanName. Add jest cases for weekly 20%/7d, weekly 25%/14d and a 30% custom plan name.

Found by review of #1183.