feat: pipeline init_metabase para desplegar Metabase + Postgres

Pipeline ejecutable que orquesta: crear red Docker, pull de imágenes,
iniciar Postgres con volume persistente, health check con retry
exponencial (pg_isready), e iniciar Metabase conectado via red interna.
Configurable con flags: --project, --metabase-port, --pg-user, etc.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/pipelines/init_metabase.md

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+---
+name: init_metabase
+kind: pipeline
+lang: go
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "func main() — Despliega stack Metabase + Postgres en Docker"
+description: "Pipeline que inicializa un contenedor Metabase con su base de datos Postgres. Crea red Docker, pull de imágenes, inicia Postgres con volume persistente, espera health check y lanza Metabase conectado."
+tags: [docker, metabase, postgres, pipeline, infra, analytics]
+uses_functions:
+  - docker_create_network_go_infra
+  - docker_pull_image_go_infra
+  - docker_run_container_go_infra
+  - docker_inspect_container_go_infra
+  - retry_with_backoff_go_core
+uses_types:
+  - container_info_go_infra
+  - network_go_docker
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [os/exec, encoding/json]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "functions/pipelines/init_metabase/main.go"
+---
+
+## Ejemplo
+
+```bash
+go run functions/pipelines/init_metabase/main.go \
+  --project analytics \
+  --metabase-port 3000 \
+  --pg-port 5432 \
+  --pg-user metabase \
+  --pg-password metabase \
+  --pg-database metabase
+```
+
+Salida JSON:
+```json
+{
+  "network_id": "abc123...",
+  "postgres_id": "def456...",
+  "metabase_id": "ghi789...",
+  "network_name": "analytics-net",
+  "postgres_name": "analytics-postgres",
+  "metabase_name": "analytics-metabase",
+  "metabase_url": "http://localhost:3000"
+}
+```
+
+## Notas
+
+El pipeline orquesta 5 pasos secuenciales:
+
+1. **Red Docker** — crea `{project}-net` con driver bridge
+2. **Pull** — descarga `postgres:16` y `metabase/metabase:latest`
+3. **Postgres** — inicia con volume persistente (named volume por defecto o bind mount con `--pg-volume`)
+4. **Health check** — retry exponencial (hasta ~34 min) con `pg_isready` dentro del contenedor
+5. **Metabase** — conecta a Postgres via red interna, expone en puerto configurable
+
+Reutiliza conceptualmente `docker_create_network`, `docker_pull_image`, `docker_run_container`, `docker_inspect_container` y `retry_with_backoff`, reimplementadas inline por ser un ejecutable independiente.
+
+Para destruir el stack:
+```bash
+docker stop analytics-metabase analytics-postgres
+docker rm analytics-metabase analytics-postgres
+docker network rm analytics-net
+```