docs: website integration guide

docs/INTEGRATION.md is the API reference for building the front end against the
sidecar: base URL, auth (Bearer / X-Api-Key / ?token=), protocol versioning, the
rich /health, the WebSocket live feed with a full event catalog, every REST query
and command (char/roster/vendors/link/towncrier/history/economy), the status-code
table, a worked character-page example, and current caveats. Payloads are the real
shapes captured during testing. Linked from the top-level README.

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

README.md

@@ -17,6 +17,7 @@ The shard never speaks WebSocket. Every world read happens on the Core thread; t
 | `patches/` | Unified diffs against stock ServUO for files we must modify rather than add. |
 | `sidecar/` | The Rust sidecar: terminates the loopback link to the shard, exposes WS + REST to the website. See `sidecar/README.md`. |
 | `tools/` | Never deployed. Test scaffolding and anything else that must not reach a server. |
+| `docs/INTEGRATION.md` | **Website integration guide** — the WebSocket feed, REST endpoints, auth, event catalog, and examples. Start here to build the front end. |
 | `docs/PLAN.md` | Implementation plan, measured performance budget, and the full data catalog. |
 | `docs/RESEARCH.md` | Original source-level research. Partly superseded — see the corrections table in `PLAN.md` §8. |
 | `docs/SHARD_PREREQS.md` | Repairs the target shard needed before any of this could load. |