fix: Fix create schedule not inserting the next scheduled date.

[bvanelli]

create_schedule creates the schedule and its rule/conditions correctly, but never inserts a row into the schedules_next_date table. The Actual frontend requires this row to compute and display the next occurrence date. Without it, the Next Date column is blank and the frontend crashes when attempting to edit the date field.

Here is the reference implementation from Actual: https://github.com/actualbudget/actual/blob/c0c2d1630ede6d58347af9e6a194dfa701f1fa37/packages/loot-core/src/server/schedules/app.ts#L288-L295

Closes #193

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.64%. Comparing base (983b463) to head (af138a2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #195      +/-   ##
==========================================
+ Coverage   97.60%   97.64%   +0.03%     
==========================================
  Files          21       21              
  Lines        3212     3222      +10     
==========================================
+ Hits         3135     3146      +11     
+ Misses         77       76       -1     

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