Get off Docker Hub, add a catalog values passthrough, fix the dind prune

Docker Hub rate-limits anonymous pulls per source IP and every node here
shares one NAT address, so a busy afternoon fails an unrelated build with
`toomanyrequests`. Nothing in this repo needs to be there.

Every base image now comes from mirror.gcr.io (python, alpine/helm,
postgres) or ghcr.io (uv, trivy). Verified digest-for-digest against
Docker Hub before switching, including the superseded postgres digest
this repo still pins, so every existing pin stays valid — same bytes,
different transport.

catalog.yaml: the three bitnami entries named `bitnamilegacy/<chart>`, a
repo alias nothing in the worker image configures, so they could never
resolve at provision time. All five entries are now `oci://` refs, which
need no `helm repo add`, and all are on latest stable:

  elasticsearch 21.3.15 -> 22.1.6     redis    20.6.2 -> 27.0.15
  postgresql    16.4.5  -> 18.8.0     podinfo  6.7.1  -> 6.14.0

Moving the chart pull is only half of it, though: a bitnami chart
defaults its own images to registry-1.docker.io. CatalogEntry gains a
`values:` dict, merged under the size's replicas and resources, so an
entry can set `global.imageRegistry` and move the image pull too. Size
wins on conflict — otherwise an entry setting replicaCount would make
every size deploy the same shape. Deep merge, because a shallow one
drops sibling keys of a shared nested map.

Bitnami charts reject a substituted registry unless
`global.security.allowInsecureImages` is set. That check is about
provenance, and the mirror serves byte-identical manifests, so it is set
deliberately and only for entries whose digests were verified.

The dind prune had `--filter until=168h` on both prunes, and it got both
cases exactly backwards. `until` reads an image's CREATED time, so it
deleted trivy every leg (a released tool image is always older than any
window) while protecting the dangling build layers it existed to remove.
Measured on node0: 21 dangling images / 5.96GB, and exactly 1 of them
older than 168h. Trivy is protected by a tag now, so the image prune
drops the filter; buildx keeps it, where age genuinely matters.

Tests: +10 unit (deep merge, precedence, no-mutation, and a guard that
fails if any catalog entry points at Docker Hub). Both new guards were
control-tested by breaking the code and watching them fail. The API test
that hardcoded `21.3.15` now reads the catalog — its subject is where
the value comes from, not what it is.

services/worker/Dockerfile

@@ -7,7 +7,7 @@
 # binaries. They are copied from pinned images rather than curl'd, so the version is a
 # reviewable line in a Dockerfile instead of a network call at build time.
 
-FROM python:3.14-slim@sha256:cea0e6040540fb2b965b6e7fb5ffa00871e632eef63719f0ea54bca189ce14a6 AS builder
+FROM mirror.gcr.io/library/python:3.14-slim@sha256:cea0e6040540fb2b965b6e7fb5ffa00871e632eef63719f0ea54bca189ce14a6 AS builder
 
 COPY --from=ghcr.io/astral-sh/uv:0.11.29@sha256:eb2843a1e56fd9e30c7276ce1a52cba86e64c7b385f5e3279a0e08e02dd058fc /uv /usr/local/bin/uv
 
@@ -30,7 +30,7 @@ p = svcforge_core.__file__; \
 sys.exit(0) if "site-packages" in p else sys.exit("not a wheel install: " + p)'
 
 # --- runtime --------------------------------------------------------------------------
-FROM python:3.14-slim@sha256:cea0e6040540fb2b965b6e7fb5ffa00871e632eef63719f0ea54bca189ce14a6
+FROM mirror.gcr.io/library/python:3.14-slim@sha256:cea0e6040540fb2b965b6e7fb5ffa00871e632eef63719f0ea54bca189ce14a6
 
 ARG BUILD_SHA=unknown
 LABEL org.opencontainers.image.title="svcforge-worker" \
@@ -45,7 +45,7 @@ COPY --from=builder --chown=10001:10001 /app /app
 # CVE-2025-68121 (crypto/tls) and CVE-2026-33186 (grpc), plus HIGH CVE-2026-35469
 # (spdystream, fixed in 0.5.1) — trivy fails the build on them and is right to.
 # Deliberately 3.x: helm 4 is a breaking change and is not a CVE fix.
-COPY --from=alpine/helm:3.21.3@sha256:35da09ba0716fc7c3cd63b6b31ee380a9c7662e95f29ab0e4ae962420afd315b /usr/bin/helm /usr/local/bin/helm
+COPY --from=mirror.gcr.io/alpine/helm:3.21.3@sha256:35da09ba0716fc7c3cd63b6b31ee380a9c7662e95f29ab0e4ae962420afd315b /usr/bin/helm /usr/local/bin/helm
 
 ENV PATH="/app/.venv/bin:$PATH" \
     PYTHONUNBUFFERED=1 \