Add resilient S3 content storage

[ty-everett]

PaperTrade currently ties its only serving pod to one Longhorn RWO content volume, so an unexpected node loss removes its sole endpoint until the volume detaches and reattaches. This change adds a Garage-compatible S3 content backend, moves new publication versions to immutable object prefixes before committing database paths, and runs production as two hard-spread replicas with a one-pod PDB and local conversion scratch space.

The production manifest also retires the obsolete ingress-nginx and PVC definitions. Its Service selects only S3-backed pods, which lets operations bring up and validate an S3 canary before switching traffic; the original retained PVC remains outside the deployment for rollback and evidence.

Validation:

• npm audit --omit=dev (0 vulnerabilities)
• npm run lint
• npm run typecheck
• npm test (31 tests)
• npm run build
• production kustomize client dry-run
• live Garage streamed put/get SHA-256 comparison and scoped cleanup
• existing production publication copy: 2,126 source files, 2,126 objects, rclone check reports 0 differences