fix: Add Configurable Alerting for Campaign Budget Thresholds

[Teejay2696]

Summary

Implemented configurable alerting for campaign budget thresholds via a scheduled cron job (CampaignBudgetAlertScheduler) that checks campaign budget consumption against configurable thresholds (defaulting to 80%), sends notifications to admins, and deduplicates alerts using audit logs.

Changed files

• app/backend/src/campaigns/campaign-budget-alert.scheduler.ts

Test plan

Run backend tests including unit tests for the campaign budget alert scheduler covering threshold crossing and de-duplication.

This PR was created as a draft by the issue solver bot. It will remain a
draft until repository CI passes.

Closes #1187

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[Cedarich]

Doing a repo-wide cleanup - closing all currently open pull requests to reset the board, not a judgement on this contribution.

Nothing is lost: this branch and every commit on it still exist, and you're welcome to reopen this PR (or open a fresh one) at any time. If this was tracking an issue, that issue is being unassigned so it goes back into the open pool - feel free to comment on it to pick the work back up.

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