A duel server: rooms, seat tokens, ledgers, and resolution when all have moved

Plain HTTP for actions and a websocket that only says "fetch again". A
room is its append-only ledger replayed from the top; the engine is
deterministic given the seed and the recorded inputs. Each seat sees a
view filtered to what the rules let it know. Bot seats are filled at
resolution time.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.gitignore

@@ -20,3 +20,6 @@ vite.config.ts.timestamp-*
 
 # Playwright MCP output
 .playwright-mcp
+
+# Duel ledgers written by the server
+/data