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Docker Hub before switching, including the superseded postgres digest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.

tests/integration/test_api.py

@@ -28,6 +28,7 @@ from fastapi import FastAPI
 
 from services.api.main import create_app
 from services.api.routes.instances import release_name_for
+from svcforge_core.domain.catalog import load_catalog
 from svcforge_core.repo.db import DictPool
 from svcforge_core.settings import Settings
 
@@ -182,8 +183,10 @@ async def test_post_returns_202_and_location(client: httpx.AsyncClient, token: s
     assert resp.headers["location"] == f"/v1/instances/{body['id']}"
     assert body["state"] == "requested"
     assert body["service_type"] == "elasticsearch"
-    # Pinned from catalog.yaml at creation time, not echoed from the request.
-    assert body["chart_version"] == "21.3.15"
+    # Pinned from catalog.yaml at creation time, not echoed from the request. Read from the
+    # catalog rather than hardcoded: the literal made a routine version bump fail here, on a
+    # test whose subject is *where the value comes from*, not what it is.
+    assert body["chart_version"] == load_catalog(CATALOG)["elasticsearch"].chart_version
     assert body["endpoint"] is None
     # The response model is an allow-list: placement details stay off the wire.
     assert "team" not in body and "namespace" not in body and "release_name" not in body