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/migrations/20260308120000_add_backup_pending/migration.sql

@@ -0,0 +1,14 @@
+-- Backup pending queue for git-based backup sync
+CREATE TABLE "BackupPending" (
+    "id" TEXT NOT NULL,
+    "resourceKind" TEXT NOT NULL,
+    "resourceName" TEXT NOT NULL,
+    "action" TEXT NOT NULL,
+    "userName" TEXT NOT NULL,
+    "yamlContent" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "BackupPending_pkey" PRIMARY KEY ("id")
+);
+
+CREATE INDEX "BackupPending_createdAt_idx" ON "BackupPending"("createdAt");