feat: support ADMIN_EMAIL and ADMIN_PASSWORD env vars for initial admin setup

Allow the first-boot admin account to be configured via ADMIN_EMAIL and
ADMIN_PASSWORD environment variables. If both are set the account is created
with those credentials; otherwise the existing random-password fallback is
used. Documented across .env.example, docker-compose.yml, Helm chart
(values.yaml, secret.yaml, deployment.yaml), and CLAUDE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chart/templates/deployment.yaml

@@ -42,6 +42,18 @@ spec:
                   name: {{ default (printf "%s-secret" (include "trek.fullname" .)) .Values.existingSecret }}
                   key: {{ .Values.existingSecretKey | default "ENCRYPTION_KEY" }}
                   optional: true
+            - name: ADMIN_EMAIL
+              valueFrom:
+                secretKeyRef:
+                  name: {{ default (printf "%s-secret" (include "trek.fullname" .)) .Values.existingSecret }}
+                  key: ADMIN_EMAIL
+                  optional: true
+            - name: ADMIN_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: {{ default (printf "%s-secret" (include "trek.fullname" .)) .Values.existingSecret }}
+                  key: ADMIN_PASSWORD
+                  optional: true
           volumeMounts:
             - name: data
               mountPath: /app/data