feat(ops): W4-B single-container packaging, DATA_DIR, backup/restore

- DATA_DIR (/data: agent-sessions, backups, exports, tmp); entrypoint chowns it
  to PUID/PGID then drops privileges via gosu; /app binary stays root read-only
- compile with --allow-read --allow-write so mounted library roots are writable
- preflight: DATA_DIR/session dir must be writable (fatal); enabled library
  roots and downloader path mappings checked read/write (warn + audit)
- --role export-mappings (mapping manifest JSON, --compare row counts) and
  --role read-only-on (automation.readOnlyReconcile=true + audit)
- scripts/backup.sh (pg_dump custom + mappings + agent sessions, SHA256SUMS,
  BACKUP_KEEP rotation) and scripts/restore.sh (checksum, refuses with live
  connections, psql single-transaction replay compatible with PG16, read-only
  reconcile on, row-count verification)
- compose: app + postgres only, data volume, env example with key generation
- docs: runbook deploy.md, backup-restore.md with verification record

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/deno.json

@@ -5,7 +5,7 @@
   "tasks": {
     "dev": "deno run -A --watch --env-file=../../.env src/main.ts",
     "start": "deno run --allow-net --allow-env --allow-sys --allow-read --env-file=../../.env src/main.ts",
-    "compile": "deno compile --frozen --node-modules-dir=none --exclude-unused-npm --allow-net --allow-env --allow-sys --allow-read=/app --include ../../packages/db/migrations --output ../../dist/umt-server src/main.ts",
+    "compile": "deno compile --frozen --node-modules-dir=none --exclude-unused-npm --allow-net --allow-env --allow-sys --allow-read --allow-write --include ../../packages/db/migrations --output ../../dist/umt-server src/main.ts",
     "test": "deno run -A npm:vitest run",
     "typecheck": "deno run -A npm:typescript/tsc --noEmit -p tsconfig.json"
   }