feat(functions): cron schedule field maps to cronPattern

[kkopanidis]

Problem

The functions UI collected a cron schedule but stored it only as inputs.event. The backend now expects canonical inputs.cronPattern, and invalid patterns were accepted without client-side feedback.

Summary

• Map cronString → inputs.cronPattern (keeps inputs.event as alias for transition)
• Load edit forms from inputs.cronPattern ?? inputs.event
• Client-side 5-field cron validation via cron-parser
• Helper text: minute hour day month weekday (UTC)

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the ui-rewrite branch

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Test plan

• Create cron function with */5 * * * *; confirm API payload includes inputs.cronPattern
• Submit invalid cron (e.g. not a cron); confirm inline validation error
• Edit an existing cron function stored with legacy inputs.event; confirm field pre-fills
• Edit schedule and save; confirm updated pattern persists