Remove Needle; stop paging on nginx 4xx

Needle scored ~chance on the golden set and never gated alerts, so drop the
sidecar, proxy handlers, UI buttons, k8s container and build step. The labelled
eval sets move to cmd/triage-eval/data.

nginx 4xx (registry 401 challenges, /oauth2/auth, scanner 405s) is now dropped
in FilterActionable instead of only being discounted, so it cannot ride along
with a real 5xx. nginx 5xx still alerts.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

build.sh

@@ -5,10 +5,6 @@ RELEASE="${RELEASE:-$(git rev-parse --short HEAD)}"
 PUBLIC_SOURCEMAPS="${PUBLIC_SOURCEMAPS:-false}"
 UPLOAD_SOURCEMAPS="${UPLOAD_SOURCEMAPS:-true}"
 
-echo "Building Needle 3 sidecar image..."
-docker build -t matst80/needle-sidecar:latest cmd/needle-sidecar
-docker push matst80/needle-sidecar:latest
-
 echo "Building otel-debug receiver image..."
 docker build \
   --build-arg "APP_RELEASE=${RELEASE}" \