R7: per-player transports + drop finished games in the load harness

Each virtual player now builds its own edge.Client (its own h2c connection
carrying both the Subscribe stream and the Execute calls), instead of every
player multiplexing over a single shared http2.Transport. The R2 trip report
traced the ~14% transport_error on game.state at 500 players to that single
shared transport; per-player connections mirror real clients and isolate the
artifact. The assembly burst and the gateway-hammer each get their own client.

playTurn now reports when a game has finished so playerLoop drops it from the
rotation (slices.DeleteFunc); once no active game remains the player idles while
still holding its stream. This stops secondary ops from hammering game_finished
on already-ended games (the other R2 harness finding).

loadtest/cmd/loadtest/main.go

@@ -24,7 +24,6 @@ import (
 	"syscall"
 	"time"
 
-	"scrabble/loadtest/internal/edge"
 	"scrabble/loadtest/internal/moves"
 	"scrabble/loadtest/internal/report"
 	"scrabble/loadtest/internal/scenario"
@@ -114,7 +113,7 @@ func cmdRun(ctx context.Context, log *slog.Logger, args []string) error {
 	log.Info("seeded", "durable", len(pool.Durables), "guest", len(pool.Guests))
 
 	rec := report.New()
-	drv := scenario.NewDriver(edge.New(*gateway), reg, rec, log)
+	drv := scenario.NewDriver(*gateway, reg, rec, log)
 	cfg := scenario.RealisticConfig{
 		Steps: steps, StepDur: *stepDur, GamesPerPlayer: *gpp,
 		Tick: *tick, SecondaryProb: *secProb,