chore: fix timezone for Go/scratch containers (shuffle-backend, pagerduty-stub)

TZ env var alone isn't enough for Alpine containers with no /usr/share/zoneinfo.
Add bind-mounts for both /etc/localtime and /usr/share/zoneinfo/Asia/Bangkok
so named TZ lookup resolves correctly. All 15 containers now show +0700.

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

Shuffle/docker-compose.yml

       - /var/run/docker.sock:/var/run/docker.sock
       - ${SHUFFLE_APP_HOTLOAD_LOCATION}:/shuffle-apps:z
       - ${SHUFFLE_FILE_LOCATION}:/shuffle-files:z
+      - /usr/share/zoneinfo/Asia/Bangkok:/etc/localtime:ro
+      - /usr/share/zoneinfo/Asia/Bangkok:/usr/share/zoneinfo/Asia/Bangkok:ro
     env_file: .env
     environment:
       - TZ=Asia/Bangkok

compose-overrides/pagerduty.stub.yml

     environment:
       - TZ=Asia/Bangkok
       - PORT=80
+    volumes:
+      - /usr/share/zoneinfo/Asia/Bangkok:/etc/localtime:ro
+      - /usr/share/zoneinfo/Asia/Bangkok:/usr/share/zoneinfo/Asia/Bangkok:ro
     ports:
       - "${PAGERDUTY_STUB_PORT:-18080}:80"
     networks: