feat(shard): Protocol 2.0 boards UI — guilds, governors, houses, players-online

Phase 2: the public UI for the four new boards, following the ChampSpawns live
pattern (snapshot via useAsync + merge SSE deltas with useShardFeed).

- Players Online widget (components/PlayersOnline.jsx): total + region breakdown
  rolled up into display buckets (data/regionBuckets.js — the one place to retune
  the grouping); live via presence.online. Placed on the Shard page, replacing the
  static players-online stat tile.
- Guilds (/site/guilds): searchable board of rosters/alliances/leaders with a
  "recently joined" strip from guild.join.
- Governors (/site/governors): one card per city with a placeholder crest
  (data/cityCrests.js — swap for real art without touching components), election
  phase badge + autoPickAt countdown, and an on-demand "past governors" term
  history (the look-back reads the ledger captured in Phase 1). Clean empty state
  when City Loyalty isn't enabled.
- Houses (/site/houses): searchable registry with decay badges; price labelled
  "placement value", not a for-sale flag.
- API client methods + nav links (Guilds / Governors / Houses).

Client build clean (240 modules).

Refs .plans/protocol2-integration.md (Phase 2).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/components/SiteHeader.jsx

@@ -13,6 +13,9 @@ const NAV = [
   { label: 'Wiki', to: '/wiki' },
   { label: 'Shard', to: '/site/shard' },
   { label: 'Champions', to: '/site/champs' },
+  { label: 'Guilds', to: '/site/guilds' },
+  { label: 'Governors', to: '/site/governors' },
+  { label: 'Houses', to: '/site/houses' },
   { label: 'About', to: '/site/about' },
 ]