fix(agent): upgrade libnghttp2-14 and remove stale .trivyignore

- Add apt-get upgrade for libnghttp2-14 (fixes CVE-2026-27135, HTTP/2
  DoS via malformed frames after session termination)
- Remove stale CVE-2026-33671 from .trivyignore (no longer detected;
  was suppressing nothing)
- Trivy now passes with zero HIGH/CRITICAL findings and an empty
  .trivyignore file

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: scottschreckengaust

agent/.trivyignore

@@ -1 +0,0 @@
-CVE-2026-33671

agent/Dockerfile

@@ -26,6 +26,8 @@ RUN apt-get update && \
         build-essential \
         ca-certificates \
         gnupg && \
+    # Upgrade base image's CVE-2026-27135 vulnerability
+    apt-get upgrade -y --no-install-recommends libnghttp2-14 && \
     # Cleanup early to keep peak disk usage low during builds.
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /var/cache/apt/archives/*