docs: rewrite the README around the three pillars and audit the docs

[Rotfuks]

What

The README is now an overview built around the platform's three pillars, styled after agentlab:

• A tagline, then an architecture diagram in light and dark variants (docs/img/architecture-{light,dark}.svg). The diagram is generated by docs/img/architecture.py; edit the script and rerun it.
• Agent Runtime, Tool Access and Model Runtime, plus an "Across all three" section. Each has a one-line summary and a table describing every component, linked to its project.
• Why Agent Platform, a quick start (AgentLab, or helm install), a docs index, and contributing guidance covering both this repository's own code and the component repositories.

The old README moves to docs/reference.md. It was audited against values.yaml, the templates and the tests, then cut from about 200 KB to about 53 KB. The audit found real errors, for example:

• Version ranges: substrate, cluster-manager, backstage, mcp-kubernetes and the kserve charts were documented with the wrong ranges.
• Examples that fail the render: valkey.enabled, agentSandbox.enabled and mcps.enabled are all rejected.
• Removed keys still documented: modelManager.route, the old dev-tag shape and the old hook images.
• Inverted mechanism: the Substrate worker image is derived from the floor of the version range, not the other way round.
• kagent metrics: documented as not served; the controller serves them on :8080.

Issue-number history, timings and narratives that repeated other docs were cut. Every inbound anchor still resolves.

Other docs:

File	Change
docs/authentication.md	Rewritten at about a third of its length. The client URL is muster.<domain>/mcp, and Giant Swarm-internal shared-configs details and non-existent values are gone.
docs/install.md	Example table corrected; the global.* table condensed to the keys an adopter must set.
docs/model-serving-image-pulls.md	Condensed; the benchmark data stays in #801.
Toolset presets, serving presets, Substrate security, chart READMEs (.gotmpl and generated)	Targeted factual fixes.
docs/kagent-v1alpha3-cutover.md	Removed. It was a one-off internal runbook for three named installations; UPGRADE.md now carries the generic steps.
Kubernetes requirement	Now stated as ≥ 1.35. The ≥ 1.33 floor was removed, because nothing in the charts, CI or tests enforced it.

Not done here

• Giving UPGRADE.md entries real versions instead of <current> → <next> headings, and pruning obsolete entries.
• Trimming the incident narratives in the chart READMEs.
• Fixing code-side drift: unused validateIngress, duplicate make targets, stale comments, and a Chart.yaml version that doesn't match the release tags.

Checklist

• Update changelog in CHANGELOG.md.
• Make sure values.yaml and values.schema.json are valid. No values changed.
• A new or materially changed serving preset states its kubernetes-cka-v2 mean score and range and links the committed result. Not applicable.

make verify-all was not run locally (the local Helm is 3.13); CI covers it.

[QuentinBisson]

Can you fix CI? Otherwise it looks good

[circleci-architect]

Published Helm chart agent-platform

4.122.1-r73c3e619t20261009122734hb56285f

Chart	agent-platform
Version	4.122.1-r73c3e619t20261009122734hb56285f
OCI reference	oci://gsoci.azurecr.io/charts/giantswarm/agent-platform:4.122.1-r73c3e619t20261009122734hb56285f
Digest	sha256:43df51e226f1e9442a3eb6386460e506f694ff2a12900db851fae1d04f127ba1
Registry	public — gsoci.azurecr.io
Git catalog	giantswarm-test-catalog (index)

Pull this chart

helm pull oci://gsoci.azurecr.io/charts/giantswarm/agent-platform --version 4.122.1-r73c3e619t20261009122734hb56285f

_{Posted by architect-orb · build 20510 · commit b56285f · updated in place on every push}