Stage 4: lobby & social (matchmaking, friends, blocks, chat+nudge, invitations, profile, email, multi-player drop-out)

Engine: multi-player drop-out-and-continue with a per-game tile disposition (remove default / return), resigned seats skipped and excluded from the win, leaver rack never revealed; 2-player behaviour unchanged.

New domains (service/store, no HTTP yet): internal/social (friend request/accept graph, per-user blocks, per-game chat with nudge as a message kind, content filter via mvdan.cc/xurls/v2 + leet/separator normaliser + phone heuristic) and internal/lobby (in-memory variant-keyed matchmaking pool, friend-game invitations invite->accept with lazy 7-day expiry). account gains profile editing and the email confirm-code flow (Mailer seam: SMTP or log mailer).

Migration 00003_social.sql + regenerated jet. main wires the new services into the server (accessors for the Stage 6 handlers); robot substitution stays in Stage 5, REST/stream/push in Stage 6/8. Docs (PLAN, ARCHITECTURE, FUNCTIONAL+ru, TESTING, README) updated.

backend/internal/config/config.go

@@ -8,6 +8,7 @@ import (
 	"strconv"
 	"time"
 
+	"scrabble/backend/internal/account"
 	"scrabble/backend/internal/game"
 	"scrabble/backend/internal/postgres"
 	"scrabble/backend/internal/telemetry"
@@ -25,6 +26,9 @@ type Config struct {
 	Telemetry telemetry.Config
 	// Game configures the game subsystem (dictionaries, sweeper, live-game cache).
 	Game game.Config
+	// SMTP configures the email relay used for confirm-codes. An empty Host
+	// selects the development log mailer (the code is logged, not sent).
+	SMTP account.SMTPConfig
 }
 
 // Defaults applied when the corresponding environment variable is unset.
@@ -67,12 +71,21 @@ func Load() (Config, error) {
 		return Config{}, err
 	}
 
+	smtp := account.SMTPConfig{
+		Host:     os.Getenv("BACKEND_SMTP_HOST"),
+		Port:     envOr("BACKEND_SMTP_PORT", "587"),
+		Username: os.Getenv("BACKEND_SMTP_USERNAME"),
+		Password: os.Getenv("BACKEND_SMTP_PASSWORD"),
+		From:     envOr("BACKEND_SMTP_FROM", "no-reply@localhost"),
+	}
+
 	c := Config{
 		HTTPAddr:  envOr("BACKEND_HTTP_ADDR", defaultHTTPAddr),
 		LogLevel:  envOr("BACKEND_LOG_LEVEL", defaultLogLevel),
 		Postgres:  pg,
 		Telemetry: tel,
 		Game:      gm,
+		SMTP:      smtp,
 	}
 	if err := c.validate(); err != nil {
 		return Config{}, err