feat: add Django backend foundation and Docker runtime

Add a Django admin-backed management layer for pobsync configs, runs,
snapshots, and schedules. Keep the existing CLI engine as the execution
source of truth, add import/run management commands, and provide SQLite
default plus optional MariaDB Docker Compose support.

src/pobsync_backend/models.py

@@ -0,0 +1,110 @@
+from __future__ import annotations
+
+from django.db import models
+
+
+class TimestampedModel(models.Model):
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        abstract = True
+
+
+class GlobalConfig(TimestampedModel):
+    name = models.CharField(max_length=64, default="default", unique=True)
+    backup_root = models.CharField(max_length=512)
+    pobsync_home = models.CharField(max_length=512, default="/opt/pobsync")
+    data = models.JSONField(default=dict, blank=True)
+
+    class Meta:
+        verbose_name = "global config"
+        verbose_name_plural = "global configs"
+
+    def __str__(self) -> str:
+        return self.name
+
+
+class HostConfig(TimestampedModel):
+    host = models.CharField(max_length=255, unique=True)
+    address = models.CharField(max_length=255)
+    enabled = models.BooleanField(default=True)
+    config = models.JSONField(default=dict, blank=True)
+
+    class Meta:
+        ordering = ["host"]
+
+    def __str__(self) -> str:
+        return self.host
+
+
+class BackupRun(models.Model):
+    class RunType(models.TextChoices):
+        SCHEDULED = "scheduled", "Scheduled"
+        MANUAL = "manual", "Manual"
+
+    class Status(models.TextChoices):
+        QUEUED = "queued", "Queued"
+        RUNNING = "running", "Running"
+        SUCCESS = "success", "Success"
+        FAILED = "failed", "Failed"
+        CANCELLED = "cancelled", "Cancelled"
+
+    host = models.ForeignKey(HostConfig, on_delete=models.PROTECT, related_name="runs")
+    run_type = models.CharField(max_length=16, choices=RunType.choices, default=RunType.SCHEDULED)
+    status = models.CharField(max_length=16, choices=Status.choices, default=Status.QUEUED)
+    started_at = models.DateTimeField(null=True, blank=True)
+    ended_at = models.DateTimeField(null=True, blank=True)
+    snapshot_path = models.CharField(max_length=1024, blank=True)
+    base_path = models.CharField(max_length=1024, blank=True)
+    rsync_exit_code = models.IntegerField(null=True, blank=True)
+    result = models.JSONField(default=dict, blank=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        ordering = ["-created_at"]
+
+    def __str__(self) -> str:
+        return f"{self.host} {self.run_type} {self.status}"
+
+
+class SnapshotRecord(models.Model):
+    class Kind(models.TextChoices):
+        SCHEDULED = "scheduled", "Scheduled"
+        MANUAL = "manual", "Manual"
+        INCOMPLETE = "incomplete", "Incomplete"
+
+    host = models.ForeignKey(HostConfig, on_delete=models.CASCADE, related_name="snapshots")
+    kind = models.CharField(max_length=16, choices=Kind.choices)
+    dirname = models.CharField(max_length=255)
+    path = models.CharField(max_length=1024)
+    status = models.CharField(max_length=32, blank=True)
+    started_at = models.DateTimeField(null=True, blank=True)
+    ended_at = models.DateTimeField(null=True, blank=True)
+    metadata = models.JSONField(default=dict, blank=True)
+    discovered_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(fields=["host", "kind", "dirname"], name="unique_snapshot_per_host_kind"),
+        ]
+        ordering = ["host__host", "-started_at", "dirname"]
+
+    def __str__(self) -> str:
+        return f"{self.host}/{self.kind}/{self.dirname}"
+
+
+class ScheduleConfig(TimestampedModel):
+    host = models.OneToOneField(HostConfig, on_delete=models.CASCADE, related_name="schedule")
+    cron_expr = models.CharField(max_length=128)
+    user = models.CharField(max_length=64, default="root")
+    enabled = models.BooleanField(default=True)
+    prune = models.BooleanField(default=False)
+    prune_max_delete = models.PositiveIntegerField(default=10)
+    prune_protect_bases = models.BooleanField(default=False)
+
+    class Meta:
+        ordering = ["host__host"]
+
+    def __str__(self) -> str:
+        return f"{self.host} {self.cron_expr}"