[ITER-1] Unblock CI gates and Dependabot queue

[seonghobae]

Goal

Restore a consistently green maintenance baseline and clear stale Dependabot PR backlog.

Deliverables

• Align workflows so required checks are deterministic on private repo.
• Rebase/triage open Dependabot PRs (chore(deps): bump actions/dependency-review-action from 46a3c492319c890177366b6ef46d6b4f89743ed4 to 3c4e3dcb1aa7874d2c16be7d79418e9b7efd6261 #1-chore(deps): bump actions/checkout from 4.3.1 to 6.0.2 #4).
• Merge safe updates with evidence.

Exit criteria

• Required checks pass on default branch.
• At least one Dependabot PR merged with green checks.
• Remaining PRs have explicit decision (merge/close) and rationale.

[coderabbitai]

🔗 Related PRs

Seongho-Bae/azure-email-communication-service-sender#2 - Add Dependabot configuration [merged]
ContextualWisdomLab/kaefa#30 - Add GitHub Actions CI workflow for R CMD check [merged]
seonghobae/xtrmETL#43 - ci: make SBOM workflow manual-only [merged]
seonghobae/xtrmETL#45 - chore: billing-independent checks [merged]
seonghobae/discord-bot#4 - chore: bootstrap repository governance and security automation baseline [merged]

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