Publish the first measured constraint cohort

[dgyy]

Parent

Part of #22.

What to build

Publish one discovery page formed from a sufficiently populated measured constraint cohort, with every membership assertion traceable to current evidence.

Acceptance criteria

• Cohort predicates are allowlisted measured conditions rather than arbitrary query combinations.
• A cohort publishes only when membership and freshness thresholds are met.
• Every listed game satisfies the same current evidence predicate.
• Falling below a threshold removes the page from the sitemap and applies
  oindex,follow without deleting useful navigation.
• The page adds a comparison and methodology rather than reproducing a card list.
• Tests cover threshold crossing, stale members, canonical URL, sitemap behavior, and unsupported combinations.

Blocked by

• Publish the first browser-game trust report #25
• Add recurring observations and automatic withdrawal #26