Peak226: document the new Prebid Server adapter - #6715

Peak226: document the new Prebid Server adapter

This rewrites the existing dev-docs/bidders/peak226.md, a 2018 stub left behind when the
original Peak226 Prebid.js adapter was removed in Prebid.js 3.0. The stub still declared a uid
param that no longer exists, and pbjs: true, which has been inaccurate since that removal.

The page now documents the new Prebid Server adapter: publisherId / placementId /
region params, banner + video + native on both site and app, per-region request splitting,
${AUCTION_PRICE} expansion, and the capability front-matter.

Related PR

• Prebid Server: New Adapter: Peak226 prebid-server#4919 — New Adapter: Peak226 (draft)

Scope

This is deliberately server-only. pbjs: false — there is currently no Peak226 adapter in
Prebid.js, and correcting that stale flag is part of this change. A Prebid.js adapter is planned;
when it lands we'll submit a follow-up docs PR adding the Prebid.js usage examples and flipping
pbjs back to true.

pbs: true becomes accurate when the linked server PR merges — happy to hold this PR until then.

Notable declarations

• dchain_supported: false — the adapter does not populate demand chain.
• ortb_blocking_supported: true and deals_supported: true — bcat/badv/bapp, battr and
  imp.pmp are forwarded to the endpoint.
• No cookie sync is documented: GVL 1202 declares usesCookies: false and omits Purpose 1, so a
  TCF-compliant CMP cannot authorize a cookie drop. Bidding is unaffected (Purpose 2 declared).