fix: Use configured timezone (Paperless, Picard, Posterizarr)

[joshymcd]

Description

Replace hardcoded TZ=Europe/Amsterdam values with TZ=${TZ} in the Paperless, Picard, and Posterizarr Compose configurations. This makes each stack honor the timezone configured in its .env file and aligns these services with the repository template.

Paperless-specific PAPERLESS_TIME_ZONE configuration is unchanged.

Related Issues

• None.

Verification

• docker compose config --quiet in services/paperless
• docker compose config --quiet in services/picard
• docker compose config --quiet in services/posterizarr
• git diff --check origin/main...HEAD

Checklist

• I have performed a self-review of my code and followed the templates structure.
• I have added verification that the stack works as expected.
• I have reviewed documentation requirements; no documentation changes are needed for this configuration fix.
• A maintainer needs to select the appropriate label because external contributors cannot apply upstream labels.

Additional Context

• None.