feat(vuln): vuln-scanner platform manifests, Flux tier, alerts, L0/L2/L3 tests

Hand-authored platform/vuln-scanner (non-gating Flux tier, digest-pinned Trivy 0.76.1 and
python 3.14.9-alpine, read-only RBAC, per-pod oauth2-proxy, internal-only cve.<domain>),
five alerts with promtool tests, R-VULN-01..09 registry entries, and vuln-* L0 checks with
mutation self-tests. src/ and the bot workflow are integrated separately.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

platform/vuln-scanner/acceptances.yaml

@@ -0,0 +1,15 @@
+# Accepted CVE risk (R-VULN-08). A list; this file is the ONLY place risk can be accepted, and it reaches
+# the scanner through the merge gate (a ConfigMap generated by kustomization.yaml).
+#
+# Each entry:
+#   - id: CVE-2026-00000                 # the CVE or advisory id, exactly as the scanner reports it
+#     image: registry/repository         # exact image match; omit only for a platform-wide acceptance
+#     reason: not reachable, feature disabled  # mandatory, a real sentence
+#     expires: 2027-02-01                # mandatory YYYY-MM-DD, at most 180 days out
+#
+# An accepted finding stays in the listing with its reason and expiry and stops counting toward the
+# critical-fix alert. When the expiry passes it reverts to open automatically. An entry with no reason
+# or no expiry, or an expiry more than 180 days out or malformed, is rejected by the merge gate
+# (conformance/tests/l0-static/vuln-acceptances-schema) and ignored at runtime with the run marked
+# degraded, so a finding is never hidden by a bad entry.
+[]