chore(ci): remove per-repo Dependabot alert workflows

[claude]

✅ Checklist

• I have followed every step in the contributing guide
• The PR title follows the convention.
• I ran and tested the code works — n/a, this PR only deletes two workflow files

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Summary

Before: two scheduled workflows in this repo posted Dependabot digests to Slack — a critical-alert check every morning at 08:00 UTC, and a summary of all open alerts on Mondays at 08:00 UTC.

After: neither runs. This reporting is handled centrally now, so the two in-repo workflows were duplicating it.

How: deletes .github/workflows/dependabot-critical-alerts.yml and .github/workflows/dependabot-weekly-summary.yml. Both were self-contained — inline shell, no shared scripts or composite actions — so nothing else in .github/ referenced them.

Dependabot itself is unchanged: .github/dependabot.yml, alerts, and version updates all keep working. This removes only the two Slack notifiers.

The ENABLE_DEPENDABOT_ALERTS repository variable existed only to switch these two workflows off. Nothing else reads it, so it can be removed from the repository settings if it's set.

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Testing

No runtime code changes — this PR only removes two scheduled workflow files. Verified that nothing else in the repo references either filename, either workflow name, or the ENABLE_DEPENDABOT_ALERTS variable.

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Changelog

Removed the two in-repo scheduled workflows that posted Dependabot digests to Slack.

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Latest commit: 2e61d4e

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.