feat: Git-based backup system replacing JSON bundle backup/restore

DB is source of truth with git as downstream replica. SSH key generated
on first start, all resource mutations committed as apply-compatible YAML.
Supports manual commit import, conflict resolution (DB wins), disaster
recovery (empty DB restores from git), and timeline branches on restore.

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

src/db/prisma/schema.prisma

@@ -299,6 +299,20 @@ model AuditEvent {
   @@index([userName])
 }
 
+// ── Backup Pending Queue ──
+
+model BackupPending {
+  id           String   @id @default(cuid())
+  resourceKind String
+  resourceName String
+  action       String   // 'create' | 'update' | 'delete'
+  userName     String
+  yamlContent  String?  @db.Text
+  createdAt    DateTime @default(now())
+
+  @@index([createdAt])
+}
+
 // ── Audit Logs ──
 
 model AuditLog {