chore(merge): merge develop into main for 9.4.0 cycle

Brings 53 develop commits (i18n, Diva, campaign, guild invites, save
transfer, return/rookie guilds, hunting tournament, JSON quest/scenario
loaders, Ghidra-derived user binary parsing, and misc fixes) onto main
now that 9.3.2 has been tagged and released.

Resolves two overlap zones:

1. Migration number collision. Main shipped 0010_fix_zero_rasta_id and
   0011_fix_stale_boost_time in 9.3.2; develop had independently
   numbered 0010_campaign..0015_tournament. The migration runner keys
   applied versions by integer, so coexisting files with the same
   numeric prefix would silently skip each other. Develop's files have
   been renumbered to 0016..0021, leaving main's 0010/0011 intact. A
   schema_version rename script is required on any server that had
   already applied the old develop numbers (only frontier.mogapedia.fr
   at the time of this merge).

2. CHANGELOG.md. Develop's in-progress feature entries move into
   [Unreleased] with updated migration references; the [9.3.2] section
   is preserved verbatim.

main.go version string bumped to 9.4.0-dev to mark the new cycle.

Full test suite (go test -race ./...) passes.

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"errors"
 	"flag"
 	"fmt"
@@ -106,7 +107,7 @@ func main() {
 		}
 	}
 
-	logger.Info(fmt.Sprintf("Starting Erupe (9.3.2-%s)", Commit()))
+	logger.Info(fmt.Sprintf("Starting Erupe (9.4.0-dev-%s)", Commit()))
 	logger.Info(fmt.Sprintf("Client Mode: %s (%d)", config.ClientMode, config.RealClientMode))
 
 	if config.Database.Password == "" {
@@ -335,6 +336,7 @@ func main() {
 		si := 0
 		ci := 0
 		count := 1
+		seenPorts := make(map[uint16]string)
 		for j, ee := range config.Entrance.Entries {
 			for i, ce := range ee.Channels {
 				sid := (4096 + si*256) + (16 + ci)
@@ -344,6 +346,13 @@ func main() {
 					count++
 					continue
 				}
+				if prev, exists := seenPorts[ce.Port]; exists {
+					preventClose(config, fmt.Sprintf("Channel %d: port %d already used by %s", count, ce.Port, prev))
+					ci++
+					count++
+					continue
+				}
+				seenPorts[ce.Port] = fmt.Sprintf("channel %d", count)
 				c := *channelserver.NewServer(&channelserver.Config{
 					ID:          uint16(sid),
 					Logger:      logger.Named("channel-" + fmt.Sprint(count)),
@@ -393,8 +402,12 @@ func main() {
 	<-sig
 
 	if !config.DisableSoftCrash {
-		for i := 0; i < 10; i++ {
-			message := fmt.Sprintf("Shutting down in %d...", 10-i)
+		countdown := config.ShutdownCountdownSeconds
+		if countdown <= 0 {
+			countdown = 10
+		}
+		for i := 0; i < countdown; i++ {
+			message := fmt.Sprintf("Shutting down in %d...", countdown-i)
 			for _, c := range channels {
 				c.BroadcastChatMessage(message)
 			}
@@ -409,8 +422,10 @@ func main() {
 	}
 
 	if config.Channel.Enabled {
+		drainCtx, drainCancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer drainCancel()
 		for _, c := range channels {
-			c.Shutdown()
+			c.ShutdownAndDrain(drainCtx)
 		}
 	}