Allow campaign owner to cancel pre-funded campaigns

[0xdevcollins]

Problem

Only admin can cancel campaigns (cancel_campaign and terminate_campaign are both admin-only). Campaign creators have no way to cancel their own campaigns before funding completes.

Current Behavior

• cancel_campaign() — admin-only
• terminate_campaign() — admin-only
• Creator has no cancel function

Expected Behavior

Add owner_cancel_campaign(campaign_id):

• Owner-only (require auth)
• Only allowed in Draft, Submitted, or Campaigning status (not after Funded)
• If Campaigning with existing pledges, trigger refund batches
• Emit CampaignCancelledByOwner event

Acceptance Criteria

• Owner can cancel in Draft/Submitted/Campaigning states
• Refunds triggered automatically if pledges exist
• Cannot cancel after Funded (milestones in progress)
• Event emitted for indexer
• Tests cover all cancel scenarios

Priority

Medium — Improves creator autonomy. Currently creators must ask admin to cancel.

Labels

crowdfunding, smart-contract, enhancement