[BUG] Remove invalid "Grafana without Prometheus" template branch

[josecelano]

Overview

Remove dead code from the Docker Compose template that handles an impossible configuration state: Grafana enabled without Prometheus. This template branch can never be executed because environment validation should reject this configuration. The code misleads readers into thinking this is a valid configuration.

Problem

The template has an {%- else %} branch for when Grafana is enabled but Prometheus is NOT:

grafana:
  depends_on:
{%- if prometheus %}
    prometheus:
      condition: service_healthy
{%- else %}
    - tracker  # <-- This branch handles an INVALID case
{%- endif %}

Why it's a bug

• Grafana requires Prometheus as its data source - it has no purpose without it
• The environment creation should fail validation if grafana.enabled = true and prometheus.enabled = false
• This template branch can NEVER be reached in valid configurations
• The code is dead code that misleads readers into thinking this is a valid configuration

Goals

• Verify environment validation rejects grafana.enabled && !prometheus.enabled
• Remove the dead {%- else %} branch from the Docker Compose template
• Simplify template to always use Prometheus dependency when Grafana is enabled

Expected Template State After Fix

grafana:
  depends_on:
    prometheus:
      condition: service_healthy

Since Grafana can only exist when Prometheus exists (enforced by validation), no conditional is needed.

Implementation Plan

1. Verify Validation - Search codebase for existing validation of Grafana/Prometheus relationship
2. Remove Dead Code - Edit templates/docker-compose/docker-compose.yml.tera to remove the {%- else %} branch
3. Verification - Run linters and E2E tests

Acceptance Criteria

• Pre-commit checks pass: ./scripts/pre-commit.sh
• Dead {%- else %} branch removed from Grafana depends_on section
• Validation exists that rejects grafana.enabled && !prometheus.enabled
• No regression in generated docker-compose.yml for valid configurations
• E2E tests pass

Related

• Parent Epic: [Epic] Docker Compose Topology Domain Model Refactoring #287
• Refactoring Plan: docs/refactors/plans/docker-compose-topology-domain-model.md
• Issue Specification: docs/issues/XXX-remove-invalid-grafana-without-prometheus-template-branch.md