docs: [#246] complete Phase 4 documentation and enable Grafana in E2E tests with retry logic

- Created comprehensive Grafana Integration Pattern ADR documenting
  all design decisions (enabled-by-default, Prometheus dependency,
  environment variable config, named volume storage, port exposure,
  manual datasource setup, future automation plans)
- Created comprehensive Grafana service guide with real config
  examples from envs/manual-test-grafana.json (600+ lines covering
  overview, configuration, disabling, accessing, initial setup,
  dashboards, verification, troubleshooting, architecture)
- Reorganized documentation: moved detailed Grafana content from
  main README to dedicated service guide, streamlined main user
  guide with brief summary and links
- Updated E2E tests to validate Prometheus and Grafana services:
  added both services to config generation, enabled validation
  flags for release and run commands
- Implemented Grafana validator retry logic to handle container
  startup delay (30 attempts × 2 seconds = 60s max wait) with
  warning logs between attempts
- Added 'devpass' to project dictionary for spell checking

Author: josecelano

docs/decisions/README.md

@@ -6,6 +6,7 @@ This directory contains architectural decision records for the Torrust Tracker D
 
 | Status        | Date       | Decision                                                                                                  | Summary                                                                                    |
 | ------------- | ---------- | --------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------ |
+| ✅ Accepted   | 2025-12-20 | [Grafana Integration Pattern](./grafana-integration-pattern.md)                                           | Enable Grafana by default with hard Prometheus dependency and environment variable config  |
 | ✅ Accepted   | 2025-12-17 | [Secrecy Crate for Sensitive Data Handling](./secrecy-crate-for-sensitive-data.md)                        | Use secrecy crate for type-safe secret handling with memory zeroing                        |
 | ✅ Accepted   | 2025-12-14 | [Database Configuration Structure in Templates](./database-configuration-structure-in-templates.md)       | Expose structured database fields in templates rather than pre-resolved connection strings |
 | ✅ Accepted   | 2025-12-13 | [Environment Variable Injection in Docker Compose](./environment-variable-injection-in-docker-compose.md) | Use .env file injection instead of hardcoded values for runtime configuration changes      |