docs: refresh CONTROLLER_REGISTRY example in PRD after #896

[ChristopherJHart]

Summary

Refreshes the CONTROLLER_REGISTRY example in dev-docs/PRD_AND_ARCHITECTURE.md so it matches the API that #896 shipped. Documentation only — no code paths touched.

Split out of #936, where it was originally bundled with an unrelated env var correction.

Problem

The example still documents the pre-refactor API:

Doc showed	Actual API after #896
CredentialSet(env_vars=[...]) positional tuple	fields={kind: ENV_VAR} mapping
auth_method="token" string	AuthMethod.TOKEN enum member
insecure_env_var absent	present — backs should_verify_ssl()
IOS-XE sets had URL only	sets carry device username/password
credential_sets=[...] list	ControllerConfig.credential_sets is a tuple

Anyone following the example to add a controller would write code that fails to construct.

Changes

Updated the SDWAN and IOS-XE entries in that code block to match nac_test/core/controller.py on main, and carried over the comment explaining that IOSXE_URL and IOSXE_HOST both map to kind="url" because the former is being phased out.

Not included

I did not add an NXOS entry to the example. The block already ends with # CC, MERAKI, FMC, ISE follow the same pattern... and has never enumerated every controller, so adding NXOS would gain little while making this PR depend on #895 merging first. Keeping it out leaves this as pure mechanical cleanup that can merge in any order.

Test plan

• Documentation-only change
• Example verified line-by-line against nac_test/core/controller.py on main
• Field names, enum member, and tuple/list types cross-checked against the ControllerConfig and CredentialSet dataclass definitions

Related

• feat(core): controller resolution refactor - single-source-of-truth #896 — the controller-resolution refactor that made this example stale
• docs: correct NX-OS Direct D2D credential env vars in PRD #936 — the NX-OS env var correction this was split out of

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🤖 AI Generation Metadata

• AI Generated: Yes
• AI Tool: claude-code
• AI Model: claude-opus-5
• AI Contribution: ~100%
• AI Reason: documentation correction
• Human Oversight: Reviewed by Christopher Hart

[oboehmer]

Thanks! We should really drop code examples from this doc ;-)