Fix invalid Systemd OnCalendar syntax (Issue #3)

[jochym]

Summary

This PR fixes an issue where the OnCalendar syntax for systemd timers was generated incorrectly when the weekday was not specified (represented by *).

Changes

• Updated cronToSystemdCalendars in src/index.ts to conditionally include the weekday in the OnCalendar string.
• According to systemd.time(7), the weekday should be omitted if it is not specifically required, as systemd does not accept * as a valid weekday specifier in this context.

Verification

• Verified that 0 9 * * * (daily at 09:00) now correctly generates OnCalendar=*-*-* 09:00:00 (previously * *-*-* 09:00:00).
• Verified that 30 8 * * 1 (Mondays at 08:30) correctly generates OnCalendar=Mon *-*-* 08:30:00.
• Validated the new syntax using systemd-analyze calendar.
• Confirmed that the project builds successfully with bun run build.

Fixes #3

[jochym]

You can check the copilot review of the same change here: jochym#1
I think the comment there is not correct, but judge for yourself.

[jochym]

@benjaminshafii can you look at this fix and maybe merge it? This is a small change.

[johnnyasantoss]

lgtm
/cc @benjaminshafii

[legacycode]

Verified ✓

Independently verified this fix — the behavior is exactly as described.
Running systemd-analyze calendar confirms it:

$ systemd-analyze calendar "* *-*-* 09:00:00"
Invalid argument ✗
$ systemd-analyze calendar "*-*-* 09:00:00"
OK — daily at 09:00 ✓
$ systemd-analyze calendar "Mon *-*-* 08:30:00"
OK — Mondays at 08:30 ✓

The fix is correct and aligns with systemd.time(7).
lgtm — hope this gets merged soon, it's a real-world breakage for anyone relying on daily timers.
Thanks @jochym for the clean fix!
/cc @benjaminshafii

[vr-one]

@jochym @benjaminshafii Thanks for the fix! Anying speaking against merging this change and release it?

[v1b3coder]

I confirm this is problem for systemd users. This PR works. Please merge.

[sharadregoti]

Please merge this PR

[jasondilworth56]

Would love to see this go in @benjaminshafii if you can get to it.