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_queue_create.go

@@ -0,0 +1,72 @@
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// JobQueueCreate creates (or verifies) the jobs table and required indices in
+// the given SQLite database, activates WAL mode, and returns a ready *JobQueue.
+// tableName is typically "jobs" but can be any valid SQLite identifier.
+//
+// Schema created:
+//
+//	CREATE TABLE IF NOT EXISTS jobs (
+//	    id TEXT PRIMARY KEY,
+//	    type TEXT NOT NULL,
+//	    payload TEXT NOT NULL DEFAULT '{}',
+//	    status TEXT NOT NULL DEFAULT 'pending',
+//	    priority INTEGER NOT NULL DEFAULT 0,
+//	    attempts INTEGER NOT NULL DEFAULT 0,
+//	    max_attempts INTEGER NOT NULL DEFAULT 3,
+//	    scheduled_at TEXT NOT NULL,
+//	    started_at TEXT,
+//	    completed_at TEXT,
+//	    result TEXT,
+//	    error TEXT,
+//	    created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now'))
+//	);
+func JobQueueCreate(db *sql.DB, tableName string) (*JobQueue, error) {
+	if db == nil {
+		return nil, fmt.Errorf("job_queue_create: db must not be nil")
+	}
+	if tableName == "" {
+		tableName = "jobs"
+	}
+
+	// Enable WAL mode for concurrent read/write access.
+	if _, err := db.Exec(`PRAGMA journal_mode=WAL`); err != nil {
+		return nil, fmt.Errorf("job_queue_create: enable WAL: %w", err)
+	}
+
+	schema := fmt.Sprintf(`
+CREATE TABLE IF NOT EXISTS %s (
+    id TEXT PRIMARY KEY,
+    type TEXT NOT NULL,
+    payload TEXT NOT NULL DEFAULT '{}',
+    status TEXT NOT NULL DEFAULT 'pending',
+    priority INTEGER NOT NULL DEFAULT 0,
+    attempts INTEGER NOT NULL DEFAULT 0,
+    max_attempts INTEGER NOT NULL DEFAULT 3,
+    scheduled_at TEXT NOT NULL,
+    started_at TEXT,
+    completed_at TEXT,
+    result TEXT,
+    error TEXT,
+    created_at TEXT NOT NULL DEFAULT (strftime('%%Y-%%m-%%dT%%H:%%M:%%SZ', 'now'))
+);
+CREATE INDEX IF NOT EXISTS idx_%s_dequeue ON %s (status, priority DESC, scheduled_at ASC) WHERE status = 'pending';
+CREATE INDEX IF NOT EXISTS idx_%s_status ON %s (status);
+CREATE INDEX IF NOT EXISTS idx_%s_type ON %s (type);
+`, tableName,
+		tableName, tableName,
+		tableName, tableName,
+		tableName, tableName,
+	)
+
+	if _, err := db.Exec(schema); err != nil {
+		return nil, fmt.Errorf("job_queue_create: create schema: %w", err)
+	}
+
+	return &JobQueue{DB: db, TableName: tableName}, nil
+}