Feature: Campaign Wizard – Required fields & progress indicator

[NathanIRL7]

Goal

The guided campaign should not be able to proceed with empty required fields; progress should be visible at a glance.

Implementation (Brief)

• Steps "Target Group" and "Offer": "Next" only with completed text.

• At completion ("Create & Save Package"): same check; if an error occurs, return to the relevant step.

• Progress bar showing step X of Y; progress bar for screen readers (ARIA).

• Error message with aria-invalid / aria-describedby next to the text fields; going back/tapping clears the message.

Acceptance Criteria

• Empty "Next" field in step 1/2 → clear German message, no step change.

• Bar shows correct percentage (1/5 … 5/5).

• After "Start New Campaign," everything is reset, including the error message.