Schedule: Fix duration parser to detect trailing numbers

[PedramNavid]

Problem

The duration parser silently ignores trailing numbers without units.

Location: src/core/schedule.rs:127-154

Input like "5m30" would parse as 5 minutes, silently ignoring the trailing 30.

Recommendation

Check if current_num is non-empty after the loop:

if !current_num.is_empty() {
    return Err(ScheduleError::InvalidInterval(format!(
        "number without unit: {}",
        s
    )));
}

Priority

Priority Fix - Silent parsing errors lead to unexpected behavior.

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Created from PR review: #28 (comment)