List observation-only sports-edge cohorts

Pro-tier. Measures two explicitly observation-only Polymarket sports cohorts without changing or feeding GET /api/v1/sports-edge-signals: wider_holder measures pre-game holder piles outside the funded route's exact raw slate admission, including recent-flow rows rejected by its event, bucket, or total caps; in_play admits only provider-confirmed live games and fails closed when the provider live-board snapshot is stale or unavailable or holder/directional evidence is stale or unavailable. Every row carries observation_only=true, provider/holder freshness and completeness fields, and the response carries a required snapshot-wide operational/unknown-completeness degraded boolean plus an accountable per-sport funnel over a closed 25-value terminal-reason vocabulary. Omitted or blank category selects all 14 registered observation sport buckets, including Table Tennis and Pickleball; those two remain outside the funded sports projection. All category and all-sports cache scopes share one global observation provider-work admission, so distinct scope keys cannot multiply concurrent provider fanout. One absolute ~25s compute deadline covers cache coordination, board/universe and primary-slate membership reads, holder cache/provider work, price/metadata evaluation, and directional reads, leaving ~5s below the public router timeout for funnel reconciliation, cleanup, and response transport. A shared pre-holder stage deadline jointly bounds those database reads and board reconciliation to the smaller of 12s or half of the absolute budget remaining when that stage starts, preserving holder/post-holder opportunity; board reads use bounded fair waves and cold holder admission gives each represented canonical sport one row before any sport repeats. Single-flight refresh contention, global provider-work admission contention, absolute deadline exhaustion before a usable cache, or pre-holder stage expiry before a usable stored universe or primary-slate membership result returns 503 with error.reason=read_model_warming. Category-resolution SQL errors, Redis coordination failures, observation-universe SQL errors, and primary-slate membership query failures return 500 internal_error instead. Once a usable universe exists, later operational or unknown-completeness board, holder, or price/metadata failures are retained as explicit terminal reasons in a degraded 200 response with degraded=true: board_source_unavailable is a completed board-source failure, board_deadline_unavailable means live-board work missed either an internal configured-scope deadline or the outer fair-wave deadline; both classify only already-started rows, so for the upcoming source read funnel.sports[].board_upcoming_status instead; provider_unavailable is an attempted holder-provider failure, and holder_deadline_unavailable is holder-stage deadline exhaustion. Directional incompleteness is cohort-specific: a wider_holder row remains emitted with terminal wider_holder_emitted and directional_status=unavailable, while an in_play row fails closed with terminal in_play_directional_unavailable. capacity_limited records intentional bounded provider-work admission in the funnel and does not by itself set degraded=true. Healthy wider_holder requests may reuse a snapshot for ~180s; in_play never serves a cached observation snapshot older than ~30s, and degraded snapshots use ~30s. The ETag is a weak semantic validator over the stable page payload, including next_cursor, with request-specific meta excluded.