feat(images): make global.imageTag reach the four single-repo services

[mosoriob]

global.imageTag was added in #109 but has no effect. Every one of the four services it names carries a non-empty tag in the chart defaults, and a per-service tag wins over the global value.

Rendering 9.0.0-beta.7 the way the cutover runbook specifies:

helm template mint charts/mint --set global.imageTag=0.1.0

ghcr.io/mintproject/graphql-engine:06492bdedd05ca3534b943739f7ffffe877851da
ghcr.io/mintproject/model-catalog-api:f711a6b49d4ed523f6fd365d1da488669b127735
mintproject/ensemble-manager:latest
(ui_react absent)

Zero of four picked up the tag.

What this changes

1. Clear the four default tags — hasura, model_catalog_api, ui_react, ensemble_manager — so global.imageTag applies.
2. Default global.imageTag to 0.1.0, the first mintproject/monorepo release. An empty default falls through to .Chart.AppVersion (1.16.3), which names no image these services publish, so a bare install would break.
3. Move ui_react and ensemble_manager to GHCR. Both still pointed at Docker Hub. The single repo does not publish there, and neither Docker Hub repo has a 0.1.0 tag.
4. Package as 9.0.0-beta.8.

Verification

A bare install — no overrides at all — now resolves:

ghcr.io/mintproject/graphql-engine:0.1.0
ghcr.io/mintproject/model-catalog-api:0.1.0
ghcr.io/mintproject/mint-ui-react:0.1.0
ghcr.io/mintproject/ensemble-manager:0.1.0

Also rendered:

• --set global.imageTag=9.9.9 reaches all four.
• --set components.hasura.image.tag=PINNED still overrides the global value, so the escape hatch is intact.
• cromo, mic_ui, mic_api, data_catalog, data_catalog_db, model_catalog_endpoint, model_catalog_explorer, ui (mint-ui-lit), postgres and postgis are unchanged.
• helm lint: 0 failed.
• helm upgrade --dry-run against the MicroK8s dev cluster: rc=0.

Impact on existing consumers

Additive. dynamo and the forks override every tag per service, so nothing changes for them until they choose to drop those overrides.

README.md is regenerated with helm-docs 1.14.2. index.yaml is regenerated by make release, which rewrites the created timestamps — the same churn as #109.

Follow-up, not in this PR

appVersion is still 1.16.3, a leftover from helm create. The documented fallback chain ends there, so it is worth setting to a real MINT version.