Security: trivy-config HIGH misconfigurations — root containers + frontend Deployment securityContext (waivers)

[SharedQA]

Summary

The trivy-config gate (added in #1317) surfaces 8 HIGH IaC/Dockerfile misconfigurations. They are pre-existing and mostly on build/test images; waived in .trivyignore (4 rule IDs, documented) so the gate stays blocking for any new or other misconfiguration. This issue tracks fixing them and removing each waiver.

Findings (4 rules / 8 occurrences)

Rule	Sev	Where	Note
AVD-DS-0002 (container runs as root)	HIGH ×4	compose/seed/Dockerfile, src/ingestion/tests/e2e/compose/Dockerfile.runner, src/ingestion/tools/declarative-connector/Dockerfile, src/ingestion/tools/toolbox/Dockerfile	build/test/tooling images — add non-root USER where feasible
AVD-KSV-0118 (Deployment missing securityContext)	HIGH ×2	src/frontend/helm/templates/deployment.yaml	real prod hardening — set runAsNonRoot, drop caps
AVD-KSV-0014 (root filesystem not read-only)	HIGH ×1	src/frontend/helm/templates/deployment.yaml	set readOnlyRootFilesystem: true
AVD-DS-0029 (apt-get without --no-install-recommends)	HIGH ×1	src/ingestion/tools/toolbox/Dockerfile	add the flag

Acceptance

• Fix the frontend Deployment securityContext (KSV-0118/0014) first — that's the genuine prod gap.
• Add non-root USER to build images where it doesn't break them; --no-install-recommends on toolbox.
• Remove each rule from .trivyignore as it's fixed. Gate stays blocking for everything else.

[SharedQA]

Re-scanned with trivy config (0.71.1) against merged main (08f0527, post-#1314). Same four rule IDs on the same files — the gears migration introduced no new misconfiguration, and the api-gateway helm templates it did change (configmap.yaml/secret.yaml) produce no HIGH finding:

• DS-0002 (root container) x4 — compose/seed/Dockerfile, e2e/compose/Dockerfile.runner, tools/declarative-connector/Dockerfile, tools/toolbox/Dockerfile
• KSV-0118 (default securityContext) — src/frontend/helm/templates/deployment.yaml
• KSV-0014 (root filesystem not read-only) — src/frontend/helm/templates/deployment.yaml
• DS-0029 (apt-get without --no-install-recommends) — tools/toolbox/Dockerfile

Total occurrences read as 7 now vs 8 before — that delta is only trivy 0.71 reporting KSV-0118 once instead of twice on the same frontend deployment.yaml (tool-version counting, same resource), not a code change. The .trivyignore waivers from #1317 remain valid. The frontend Deployment securityContext (KSV-0118/0014) is still the one genuine prod-hardening item to fix first.