Add an end-to-end TCP acceptance harness (issue #15) (#20)

Stand up the real AuthoritativeServer behind the real TCP transport on a
loopback port and drive real SyntheticProtocolClient sockets through it, so the
matrix is exercised over an actual connection rather than in-memory fakes.

Covers the baseline-protocol, TCP-compatibility, and interest-management
sections: welcome->hello->sessionReady handshake, unique/non-spoofable
server-owned ids, malformed and oversized rejection before mutation, rate-limit
tripping, transform/playerState/worldState relay, action events not
replay-cached to late joiners, disconnect/reconnect leaving no stale session,
same-cell relay vs distant interest filtering, multi-client no cross-cell spam,
and handshake-timeout reaping.

The harness runs for real wherever loopback TCP can bind (dev machines, the
self-hosted runner) and skips cleanly otherwise. Wired into a self-hosted CI
job gated by the runtime-policy guard. 60s idle-timeout, 32/64-client load /
packet-loss / reconnect-churn, and GNS sections remain follow-ups.

server/README.md

@@ -26,6 +26,15 @@ dotnet run --project CommonwealthOnline.Server.csproj -- serve --config commonwe
 
 `start.bat` and `start.sh` prefer a published apphost, then a framework-dependent DLL, then `dotnet run` in a source checkout.
 
+### Tests
+
+- `tests/` — fast in-memory unit/component tests over the authoritative core (run in the `CSharp Server Gate` CI).
+- `acceptance/` — end-to-end acceptance harness (issue #15): stands up the real server behind the real TCP transport on a loopback port and drives real client sockets through the baseline-protocol, TCP-compatibility, and interest-management matrix sections. Runs in the `Acceptance (end-to-end TCP)` CI, or locally:
+
+```bash
+dotnet run --project acceptance/CommonwealthOnline.Server.Acceptance.csproj -c Release
+```
+
 ## Config
 
 Generate defaults: