feat(reporting): nielsen_audio demographic system + radio reconciliation guide

[bokelley]

Summary

Implements the WG-ratified #6139 decisions (radio/broadcast measurement packet, approved — outcome recorded on the issue):

• nielsen_audio enters demographic-system.json — same P/M/W notation scheme as Nielsen TV, measured on the PPM/diary radio panel. Enum + enumDescriptions entry, and the enum's description broadened to audio channels with the notation-vs-provider line stated explicitly.
• RAJAR stays a measurement_source, not a notation system — per the author's own resolution on the Radio: delivery-time audience-currency declaration — demographic_system placement + audio measurement systems #6139 thread (withdrawn from the notation ask; delivery-forecast.json already lists rajar in measurement_source examples).
• Radio channel guide gains the reconciliation contract (radio.mdx, replacing the bare Radio measurement: delayed delivery and reconciliation contract #6167 pointer): the three declarations — notation (demographic_system), provider identity (row-level measurement_source), maturation (measurement_windows reuse per the Radio measurement: delayed delivery and reconciliation contract #6167 ratification; no impression_phase) — with a worked committed-metric ↔ delivery-row example and the weekly-cadence optimization-eligibility gate.

Dependency note

The delivery-row example references row-level measurement_source, which ships in #6241 (the ratified #6139 decision 1 rides there because the OOH block needs the lane immediately). Merge #6241 first, or accept a brief window where the guide references a field that lands days later — schema changes here are independent either way.

Changeset included (minor). Refs #6139, #6167.

🤖 Generated with Claude Code

[aao-secretariat]

Ladon verdict: Escalate to human review

Escalate — gated path touched without required approval.

This PR modifies static/schemas/source/enums/demographic-system.json, which falls under the repo's hard, path-based approval gate (gated_paths: true). review_decision is REVIEW_REQUIRED, not APPROVED, so the gate is not satisfied and the decision table row 2 forces escalate (no critical/high findings exist to make this request-changes).

The change itself looks coherent: nielsen_audio is added as a new enum value with a P/M/W notation description, the enum scope is broadened to audio, and it ships a correct minor (additive/Normative) changeset. This is a Normative, non-breaking addition — not a breaking-class change — so the breaking-change hard gate does not independently apply. Schema↔docs coherence largely holds against the measurement_source/measurement_windows/is_final/finalized_at contracts.

Medium findings (surfaced for the human reviewer):

• docs/creative/channels/radio.mdx:158 — Docs name a nonexistent field reporting_capabilities.reporting_frequencies. Should be corrected before merge.

Escalation reason:

• Modifies gated path static/schemas/source/enums/demographic-system.json; requires human/CODEOWNERS review (review_decision is REVIEW_REQUIRED, not APPROVED).

Medium findings

• docs/creative/channels/radio.mdx:158 — Docs name a nonexistent field reporting_capabilities.reporting_frequencies

Why human review

• Modifies gated path static/schemas/source/enums/demographic-system.json (matches static/schemas/source/**); review_decision is REVIEW_REQUIRED, not APPROVED — human/CODEOWNERS review required.
• This PR touches a path under a hard, non-overridable approval gate (static/schemas/source/enums/demographic-system.json (modified) matches static/schemas/source/**) and the current GitHub review decision is 'REVIEW_REQUIRED', not APPROVED. This is a hard gate enforced in code — Ladon cannot auto-approve until a human/CODEOWNERS approval is recorded, regardless of how clean the diff is.