Sanitize committed Slack credentials in environment templates

[Copilot]

This PR removes Slack webhook credentials that were committed in project env files. It keeps the existing configuration contract while replacing sensitive values with safe placeholders.

• Credential sanitization

  • Replaced hardcoded SLACK_TOKEN values in:
    • resources/dev.env
    • resources/docker.env
  • Preserved variable names and file structure to avoid runtime/config integration changes.

• Template guidance

  • Added inline comments clarifying the expected value format for SLACK_TOKEN (base64-encoded webhook URL), so contributors can populate local values without reintroducing secrets.

• Resulting env shape (example)

  PROMETHEUS_URL="http://localhost:9090"
  # Base64 da webhook URL do Slack (ex.: echo -n "<webhook_url>" | base64)
  SLACK_TOKEN="REPLACE_WITH_BASE64_ENCODED_SLACK_WEBHOOK_URL"