docs: give delegation readers a complete verifiable first example

[imran-siddique]

The first commands referenced repository files without a checkout, omitted a usable trusted root, and promised scope escalation from an edit that fails signature verification first. The quickstart now includes its setup and one complete chain generator, retains the root independently, and demonstrates both an untrusted-root rejection and a correctly signed overbroad grant.

The homepage leads to that local result. The architecture page follows the inbound implementation's ordering and distinguishes chain validation, holder authentication, local policy, appraisal, sealed payload handling, and decision provenance. Software assurance and offline replay limits are explicit. The docs deployment now copies SPONSORS.md, which navigation already referenced.

Validation: the exact Python tutorial block passes; its saved chain verifies through the CLI with the expected two-hop read-only leaf result. Ruff passes for the new test. MkDocs builds successfully. No runtime changes; full CI and deployed visual verification follow.

[imran-siddique]

@agentrust-io/maintainers please review this PR and submit an approving review if the changes look correct. All checks are green; maintainer approval is still required to merge.

Please check the complete quickstart, its trusted-root and signed scope-escalation examples, and the architecture diagram's ordering against the inbound runtime. The documented example is exercised in CI.