Enable Grafana OAuth email lookup to reuse existing users

Without this, GitHub OAuth creates a new Grafana user on every login
instead of linking to the existing account by email.

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

infrastructure/docker-compose.yml

@@ -154,6 +154,7 @@ services:
       GF_AUTH_GITHUB_CLIENT_SECRET: ${GF_AUTH_GITHUB_CLIENT_SECRET:-}
       GF_AUTH_GITHUB_ALLOWED_ORGANIZATIONS: trails-cool
       GF_AUTH_GITHUB_SCOPES: user:email,read:org
+      GF_AUTH_OAUTH_ALLOW_INSECURE_EMAIL_LOOKUP: "true"
       GF_AUTH_DISABLE_LOGIN_FORM: "true"
       GF_SMTP_ENABLED: "true"
       GF_SMTP_HOST: ${GF_SMTP_HOST:-}