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_status.md

@@ -0,0 +1,39 @@
+---
+name: job_status_summary
+kind: function
+lang: go
+domain: infra
+version: "1.0.0"
+purity: pure
+signature: "func JobStatusSummary(counts map[string]int) string"
+description: "Formatea un mapa de status→conteo en un resumen legible. Siempre incluye los cinco estados canonicos en orden fijo: pending, running, completed, failed, dead."
+tags: [job, queue, status, summary, format, pure, infra]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: [fmt, strings]
+params:
+  - name: counts
+    desc: "mapa de nombre de status (pending/running/completed/failed/dead) a numero de jobs en ese estado"
+output: "string formateado 'pending: N, running: N, completed: N, failed: N, dead: N'"
+tested: true
+tests:
+  - "job_status_summary_format"
+  - "job_status_summary_empty_map"
+test_file_path: "functions/infra/job_queue_test.go"
+file_path: "functions/infra/job_status.go"
+---
+
+## Ejemplo
+
+```go
+counts := map[string]int{"pending": 5, "running": 2, "completed": 10}
+summary := JobStatusSummary(counts)
+// "pending: 5, running: 2, completed: 10, failed: 0, dead: 0"
+```
+
+## Notas
+
+Funcion pura. Los estados no presentes en el mapa se tratan como 0. El orden de salida es siempre fijo: pending, running, completed, failed, dead.