fix(buyer): enrich incremental discovery peers

[kotevcode]

Summary

• keep fast metadata-only peer discovery emits for first paint
• queue non-blocking on-chain enrichment for each incremental partial peer batch
• emit a second peers:discovered update after chain stats/reputation are available so buyer.state.json refreshes sooner
• add a unit test for incremental enrichment emits

Validation

• corepack pnpm --filter=@antseed/node build
• corepack pnpm --filter=@antseed/node test