Phase 4: Webhooks, Backup/Restore UI, Onboarding/Tutorial

- Webhooks Backend: model, schema, service (HMAC-SHA256, httpx), routes, event bus dispatcher, migration 0042
- Webhooks Frontend: SettingsWebhooksPage (CRUD, test button, event multi-select), API client
- Backup/Restore Backend: model, schema, service (pg_dump/pg_restore), routes (admin-only), migration 0043
- Backup/Restore Frontend: SettingsBackupPage (create, list, restore dialog with RESTORE confirmation, auto-refresh)
- Onboarding: OnboardingTour (8 steps, custom CSS overlay), WelcomeDialog, onboardingStore (zustand + localStorage)
- Onboarding integrated into AppShell
- Routes: /settings/webhooks, /settings/backup registered
- Settings nav: Webhooks, Backup & Restore entries added
- Migration conflict fixed: 0042_webhooks → 0043_backups chain

app/models/backup.py

@@ -0,0 +1,46 @@
+"""Backup model — tracks database backup records per tenant."""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import BigInteger, DateTime, String, Text
+from sqlalchemy.dialects.postgresql import UUID as PGUUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.core.db import Base, TenantMixin
+
+
+class Backup(Base, TenantMixin):
+    """Database backup record scoped to a tenant.
+
+    Tracks pg_dump backups with status, file location, and error details.
+    """
+
+    __tablename__ = "backups"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+
+    # ── Identity ──
+    filename: Mapped[str] = mapped_column(String(255), nullable=False)
+    size_bytes: Mapped[int | None] = mapped_column(BigInteger, nullable=True, default=None)
+
+    # ── Status ──
+    status: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="pending"
+    )  # pending, completed, failed
+    error_message: Mapped[str | None] = mapped_column(Text, nullable=True, default=None)
+
+    # ── Audit ──
+    created_by: Mapped[uuid.UUID | None] = mapped_column(
+        PGUUID(as_uuid=True), nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, default=datetime.utcnow
+    )
+    completed_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True, default=None
+    )