docs(docker): Hub pages for aio + ml, and the image table in the README

picpeak/ml has an empty Hub overview and picpeak/aio has none at all,
while backend and frontend carry hand-written ones — so the two newest
images are the two with nothing on their registry page.

Adds .github/dockerhub/{aio,ml}.md as the source of those pages and a
dockerhub-descriptions job that pushes them on every main merge, so the
page cannot drift from the release it describes. backend/frontend stay
hand-maintained for now: capturing their current Hub text into files is
a prerequisite, not a side effect of this change.

README gains a registry table for all four images (both registries share
digests and tags), the org-move callout lists the full set, and the
feature list finally mentions People in this gallery, which shipped in
#1074 without a README line.

.github/workflows/README-DOCKER.md

@@ -1,6 +1,6 @@
 # Docker Build and Push Workflow
 
-This GitHub Actions workflow automatically builds and pushes Docker images for the backend, the frontend, and the all-in-one image to GitHub Container Registry (ghcr.io).
+This GitHub Actions workflow automatically builds and pushes Docker images for the backend, the frontend, the all-in-one image and the optional ML sidecar to GitHub Container Registry (ghcr.io). On the canonical org repo every one of them is mirrored to Docker Hub as `docker.io/picpeak/{backend,frontend,aio,ml}`; forks build the same images GHCR-only.
 
 The **all-in-one image** (`<repo>/aio`, built from `Dockerfile.aio` at the repo root, #1042) bundles the backend and the built frontend into a single container with SQLite as the default engine — one `docker run`, no compose. It follows the same per-arch build → digest-merge → per-version tag scheme as the other two images, is mirrored to Docker Hub (`docker.io/picpeak/aio`) alongside GHCR on the canonical org repo, and every PR additionally runs a `smoke-aio` job that boots the image and asserts the SPA shell, brand-title rendering, immutable asset caching, and the SQLite engine resolution.
 
@@ -12,6 +12,7 @@ The **all-in-one image** (`<repo>/aio`, built from `Dockerfile.aio` at the repo
 - 🔒 **Security scanning** with Trivy vulnerability scanner
 - 💾 **Build caching** for faster subsequent builds
 - 📊 **Build summaries** in GitHub Actions UI
+- 📝 **Docker Hub pages** for `aio` and `ml` synced from `.github/dockerhub/*.md` on every `main` merge (`dockerhub-descriptions` job). `backend` and `frontend` pages are still hand-maintained in the Hub UI — add `.github/dockerhub/{backend,frontend}.md` with their current text before putting them under the same job.
 
 ## Authentication
 
@@ -54,6 +55,11 @@ docker pull ghcr.io/picpeak/picpeak/backend:v1.0.0
 
 # Pull for specific architecture
 docker pull --platform linux/arm64 ghcr.io/picpeak/picpeak/backend:latest
+
+# The same images on Docker Hub (identical tags, identical digests)
+docker pull picpeak/backend:latest
+docker pull picpeak/aio:stable
+docker pull picpeak/ml:stable
 ```
 
 ### Using in Docker Compose