feat: cola de jobs asincrona basada en SQLite (issue 0013)

Implementa el subsistema completo de background jobs para apps Go en el
dominio infra. 9 funciones + 3 tipos + 17 tests, todos pasando.

- Tipos: Job (product), JobQueue (product), JobStatus (sum) con
  JobHandler, EnqueueOption y WorkerOption usando functional options pattern
- job_queue_create: CREATE TABLE + indices + WAL mode
- job_enqueue: INSERT con UUID (github.com/google/uuid), WithPriority/WithScheduledAt/WithMaxAttempts
- job_dequeue: SELECT+UPDATE atomico en transaccion exclusiva, filtro por jobTypes
- job_complete / job_fail: transiciones de estado; fail → dead cuando attempts >= max_attempts
- job_status_summary: pura, formatea conteo de jobs por estado
- job_worker: poll loop bloqueante, context-cancelable, graceful shutdown
- job_worker_pool: N workers con golang.org/x/sync/errgroup
- job_cleanup: DELETE jobs terminales mas viejos que olderThan

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

functions/infra/job_enqueue.md

@@ -0,0 +1,48 @@
+---
+name: job_enqueue
+kind: function
+lang: go
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "func JobEnqueue(q *JobQueue, jobType string, payload string, opts ...EnqueueOption) (string, error)"
+description: "Inserta un nuevo job en la cola con UUID generado, tipo, payload JSON y opciones. Retorna el UUID del job. Opciones: WithPriority, WithScheduledAt, WithMaxAttempts."
+tags: [job, queue, enqueue, insert, async, background, infra, sqlite]
+uses_functions: []
+uses_types: [job_queue_go_infra]
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [fmt, time, github.com/google/uuid]
+params:
+  - name: q
+    desc: "cola de jobs creada con JobQueueCreate"
+  - name: jobType
+    desc: "identificador del tipo de trabajo (ej: 'send_email', 'resize_image')"
+  - name: payload
+    desc: "JSON string con los datos del job; si vacio se usa '{}'"
+  - name: opts
+    desc: "opciones: WithPriority(n), WithScheduledAt(t), WithMaxAttempts(n)"
+output: "UUID del job insertado como string"
+tested: true
+tests:
+  - "enqueue_dequeue_atomicidad"
+  - "dequeue_priority_order"
+  - "dequeue_jobtype_filter"
+  - "dequeue_scheduled_in_future_waits"
+test_file_path: "functions/infra/job_queue_test.go"
+file_path: "functions/infra/job_enqueue.go"
+---
+
+## Ejemplo
+
+```go
+id, err := JobEnqueue(q, "send_email", `{"to":"user@example.com"}`,
+    WithPriority(5),
+    WithMaxAttempts(5),
+)
+```
+
+## Notas
+
+Usa `github.com/google/uuid` para generar el ID. El payload por defecto es "{}". El campo `scheduled_at` por defecto es `time.Now().UTC()`. La prioridad mas alta se procesa primero (ORDER BY priority DESC).