Develop - #1345

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# Modernize backend: Django 4.2 · Celery 5 · Python 3.11 · PostgreSQL 16 · TF 2.15 / CUDA 12

## Summary
Brings Rodan's backend off its end-of-life stack and onto current, H100-capable infrastructure. Upgrades the web/framework layer, the database, and the GPU job runtime, adapts the container/k8s deployment accordingly, and fixes a set of regressions surfaced by the upgrades. 18 commits, ~129 files.

## Motivation
The old stack (Django 2.0, Celery 4.4, Python 3.7, PostgreSQL 9.6, and CUDA/TF builds targeting pre-Hopper GPUs) no longer installs cleanly, receives no security fixes, and can't run on the current H100 (sm_90) hardware. This branch is the coordinated upgrade of all of those at once.

## What's changed

**Framework (Phase 1)**
- Django 2.0 → **4.2.16**, DRF → **3.15.2**, djoser → 2.2, Celery 4.4 → **5.3.6**, Python 3.7 → **3.11**, numpy → 1.26.4.
- Realtime layer migrated from `ws4redis` → **Django Channels 4** (ASGI `ProtocolTypeRouter` + a broadcast consumer relaying the redis pub/sub channel).
- `gamera4` rebuilt for py3.11.

**Database**
- PostgreSQL 9.6 → **16** (required by Django 4.2). Includes a dump/restore cutover runbook (`k8s/POSTGRES_UPGRADE.md`); `postgres/Dockerfile` now `FROM postgres:16`.

**GPU jobs (Phase 3)**
- GPU job image rebuilt on **TensorFlow 2.15 / CUDA 12 / Python 3.11** for H100.
- `text_alignment` ported to py3.11 / TF 2.15 (upstream calamari-ocr 2.3.1).

**Containerization / k8s**
- Image chain rebuilt (`rodan-python3-celery` → `rodan-main` → `nginx`; plus client, gpu-celery, postgres, iipsrv) and all k8s manifests updated; GPU pod gets MIG visibility and `compute,utility` capabilities.

**CI/CD**
- `build-and-deploy` and `build-ci-jobs` workflows; CI test fixes.

**Bug fixes surfaced by the upgrade**
- **List filtering (`filter`→`filterset`)** — django-filter 24.3 ignores the legacy `filter_fields`/`filter_class`; renamed to `filterset_fields`/`filterset_class` across all list views (restores `?project=` and other filters), fixed 3 filter-method lambda signatures, and **restored object-level list scoping** via a guardian-based `ObjectPermissionsFilter` in `DEFAULT_FILTER_BACKENDS` (a list with no `?project=` no longer leaks every project's rows).
- **Interactive editor open** — per-key template cache fix so a second editor open per worker doesn't 500.
- **Job import guard**, **ASGI startup**, `is`→`==` identity check, gpu-celery CUDA env.

## Breaking changes / migration notes
- **Requires the PostgreSQL 9.6→16 dump/restore** before deploy (see `k8s/POSTGRES_UPGRADE.md`).
- **All images must be rebuilt** — base-image chain, Python, and CUDA/TF versions all moved.
- Deploy is triggered by a `v*` tag or a manual `build-and-deploy` dispatch (merging to `develop` only builds `nightly`/`sha-` images).

## Testing & validation
- CI test suite green on the branch.
- All automated job types validated against real DB rows + PVC files via a replay harness; both interactive editors (Neon, Pixel.js) verified end-to-end in a real browser on the modernized stack.
- Live distributed end-to-end workflow run passed on the k3s cluster.