docs(link): the player-vendor marketplace (Protocol 3.0 §8)

Documents order 5b across the four repos, and records what building it changed
about §8 as designed.

- NEW website/MARKETPLACE.md — the operator guide: what the pages must say out
  loud and why, the privacy contract (the player's in-game Vendor Search toggle
  wins, and no admin setting overrides it), the Bridge.cfg knobs and how they
  trade against each other, and the measured sweep costs.
- INTEGRATION.md — catalog entry for vendor.listing / vendor.listing.remove with
  its six consumer gotchas, and the GET /market REST section (the sidecar's only
  paged read, and why it orders by serial rather than shop name).
- BACKEND_DESIGN.md — shard_vendors / shard_vendor_items, the routes, and the
  marketplace search as the only rate-limited public read.
- SHARD_VISIBILITY.md — why the market's fields default to Everyone (the in-game
  gump already shows exactly that set), why location is one setting covering
  four things, and why hiding the owner name without the owner id achieves
  nothing.
- PLAN.md — the amortized round-robin as the one sweep pattern the bridge did not
  previously have, and an update to §7's cliloc note: pushing name resolution to
  the plugin was never an option, because ServUO cannot read a modern client's
  compressed cliloc files either.
- v3.md §8.8 — the four things the build settled differently, chief among them
  that §8.1's FLAT location payload would have made Part A's pre-wired
  market.location rule inert, exactly like the characterName miss one part
  earlier.

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

README.md

@@ -20,6 +20,9 @@ ci/        cross-cutting CI/quality notes
 | [HERO_EDITOR.md](website/HERO_EDITOR.md) | Hero canvas editor feature spec |
 | [WIKI_UPGRADE.md](website/WIKI_UPGRADE.md) | Wiki subsystem upgrade notes |
 | [SHARD_VISIBILITY.md](website/SHARD_VISIBILITY.md) | Who sees which shard data — the admin-configurable audience framework |
+| [SPAWN_ATLAS.md](website/SPAWN_ATLAS.md) | The bestiary / spawn atlas: what the shard contains, parsed from its own ServUO tree |
+| [CLILOCS.md](website/CLILOCS.md) | UO's id → name table: converting one from your client so items have names |
+| [MARKETPLACE.md](website/MARKETPLACE.md) | The player-vendor index: how it is gathered, what it costs, how to tune it |
 | [website-README.md](website/website-README.md) | Snapshot of the website repo's README (setup/run reference) |
 | [PROJECT_TREE.md](website/PROJECT_TREE.md) | Auto-generated snapshot of the repo's tracked file layout |