chore(tra-974): drop dead BACKEND_LOG_LEVEL key from backend chart

The trakrf-backend logger reads bare LOG_LEVEL via os.Getenv
(logger/config.go) — there is no BACKEND_ prefix scheme, so the chart's
config.logLevel → BACKEND_LOG_LEVEL ConfigMap key was never read by the
backend (confirmed against the backend source). PR #157 added the real
LOG_LEVEL emission (config.runtimeLogLevel); this removes the misleading
dead key and its now-orphaned config.logLevel value so the chart is honest.

No functional change — BACKEND_LOG_LEVEL was inert. Removing it does change
both envs' rendered ConfigMap (key drops out), so the next apply-root-app.sh
gke rolls the prod backend pod once (clean restart, no behavior change);
preview keeps LOG_LEVEL=info via config.runtimeLogLevel.

Verified via helm template: BACKEND_LOG_LEVEL absent from all renders;
LOG_LEVEL=info still emits when runtimeLogLevel is set; chart renders clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Mike Stankavich

helm/trakrf-backend/templates/configmap.yaml

@@ -7,12 +7,10 @@ metadata:
 data:
   APP_ENV: {{ .Values.config.appEnv | quote }}
   ENVIRONMENT_LABEL: {{ .Values.config.environmentLabel | quote }}
-  BACKEND_LOG_LEVEL: {{ .Values.config.logLevel | quote }}
 {{- with .Values.config.runtimeLogLevel }}
-  # LOG_LEVEL is the runtime level the Go backend logger reads (logger/config.go);
-  # BACKEND_LOG_LEVEL above is legacy and unread by the current backend. Emitted
-  # only when set, so envs that omit it (prod) keep their APP_ENV→warn default and
-  # render no LOG_LEVEL key. Set per-env via the root app (preview→info). TRA-974.
+  # LOG_LEVEL is the runtime level the Go backend logger reads (logger/config.go).
+  # Emitted only when set, so envs that omit it (prod) keep their APP_ENV→warn
+  # default and render no LOG_LEVEL key. Set per-env via the root app (preview→info).
   LOG_LEVEL: {{ . | quote }}
 {{- end }}
   SERVICE_NAME: {{ .Values.config.serviceName | quote }}

helm/trakrf-backend/values.yaml

@@ -139,12 +139,10 @@ mqtt:
 # Non-secret config (ConfigMap)
 config:
   appEnv: production
-  logLevel: info
   # runtimeLogLevel → the LOG_LEVEL env the Go backend logger actually reads
-  # (logger/config.go). Empty = inherit the backend's APP_ENV-based default
-  # (production→warn, dev/preview→debug). Set per-env (preview→info) to pin a
-  # level. NOTE: logLevel above feeds the legacy BACKEND_LOG_LEVEL key, which the
-  # current backend does NOT read — dead-key cleanup tracked in TRA-974.
+  # (logger/config.go, bare os.Getenv — no BACKEND_ prefix scheme). Empty =
+  # inherit the backend's APP_ENV-based default (production→warn, dev/preview→
+  # debug). Set per-env (preview→info) to pin a level.
   runtimeLogLevel: ""
   serviceName: trakrf-backend
   corsOrigin: ""