Remove mock bidder credentials from creative-opportunities.toml #697

Context

creative-opportunities.toml currently contains inline PBS bidder params under [slot.providers.pbs.bidders] for all three slots:

[slot.providers.pbs.bidders]
mocktioneer = { bid = 2.00 }
criteo = { networkId = 123456, pubid = "123456" }

These params are wired directly into the OpenRTB imp.ext.prebid.bidder map and sent to PBS on every real auction request. When inline bidder params are present, the PBS stored-request fallback (imp.ext.prebid.storedrequest) is never set — they are mutually exclusive.

Problem

• mocktioneer is a test bidder and must not appear in production config
• criteo credentials are placeholder values (networkId = 123456) that will cause PBS to reject or misroute bids
• Per the server-side ad templates design spec §4.1, PBS bidder params belong in PBS stored requests keyed by slot ID, not in creative-opportunities.toml

Action

• Remove all [slot.providers.pbs.bidders] sections from creative-opportunities.toml
• Confirm corresponding PBS stored requests exist for each slot ID before go-live
• Remove PbsSlotParams struct and SlotProviders.pbs field from creative_opportunities.rs if inline PBS params are not an intended feature

Parent: #677