refactor(controller): apply controller settings by rebuilding the channel set

Giving each controller a Reload method worked for the notification pipes, which
only hold values, but not for the two bot channels: the NapCat client is stopped
through a sync.Once and the Telegram polling context is created with the
controller, so neither can be re-pointed once running. It also meant five
bespoke implementations of the same idea.

Replace the whole set instead. Manager.ReplaceAll swaps in a freshly built set
under the registry lock, stops the outgoing controllers outside it, and starts
the incoming ones off the calling goroutine so a slow handshake does not hold
the settings request open. ReplaceAll is now the only way controllers are
installed: Register is gone, because a lone registration would slip a controller
in without recording the settings it was built from, which is what NeedsRebuild
compares against.

The rebuild runs from the reload hook and only fires when the controllerMethod
section actually changed, so saving a message template or a webhook endpoint
leaves the channels alone. NeedsRebuild compares the whole section by value, and
a test pins that reloading a file reproduces it exactly — a default applied
inconsistently would make every save look like a controller change and tear down
every channel.

With controllers immutable after construction and replaced wholesale, the atomic
pointers and Reload methods have no writers left, so they are gone and the pipes
return to plain fields. notifyReload now serializes hook execution for the same
reason: a hook mutates process-wide state, and two overlapping settings updates
would otherwise each decide to rebuild from their own view of what was applied.

Kept from that work: applyEmailProxy restores gomail's default dialer when
networkUseProxy is turned off. The old constructor only ever installed the proxy
dialer, so switching the flag back left SMTP tunnelled through a proxy with no
way to undo it short of a restart.

Documents the resulting behaviour in the README under "What applies without a
restart".

main.go

@@ -66,9 +66,17 @@ func main() {
 	config.OnReload(func(updated *config.Config) {
 		postLog.SetDebugMode(updated.System.DebugMode)
 
-		if mgr := controller.GetManager(); mgr != nil {
-			mgr.ReloadAll()
+		mgr := controller.GetManager()
+		if mgr == nil || !mgr.NeedsRebuild(updated.ControllerMethod) {
+			return
 		}
+
+		// Controller settings changed. Each controller reads its settings into
+		// fields when it is built, and the NapCat and Telegram ones own
+		// connections that cannot be re-pointed, so the change is applied by
+		// replacing the whole set rather than reconfiguring it in place.
+		postLog.Info("Controller settings changed; rebuilding every channel")
+		mgr.ReplaceAll(buildControllers(updated), updated.ControllerMethod)
 	})
 
 	dbPath := cfg.DBPath
@@ -212,83 +220,28 @@ func startWebhookServer(cfg *config.Config) {
 	}()
 }
 
-// initControllers initializes and starts all configured controllers.
+// buildControllers constructs one controller per channel from the given
+// configuration. The set is built fresh whenever controller settings change,
+// because a controller reads its settings once at construction and two of them
+// own connections that cannot be re-pointed.
+func buildControllers(cfg *config.Config) []controller.Controller {
+	return []controller.Controller{
+		qq_napcat.NewQQController(cfg.ControllerMethod.QQ),
+		telegram.NewTelegramController(cfg.ControllerMethod.Telegram),
+		pipes.NewEmailController(cfg.ControllerMethod.Email),
+		pipes.NewNtfyController(cfg.ControllerMethod.Ntfy),
+		pipes.NewWebhookController(cfg.ControllerMethod.Webhook),
+	}
+}
+
+// initControllers installs the initial controller set.
 func initControllers() {
 	cfg := config.Current()
 	mgr := controller.GetManager()
-	if mgr == nil {
+	if mgr == nil || cfg == nil {
 		return
 	}
-
-	// QQ (Napcat) controller.
-	qqCtrl := qq_napcat.NewQQController(cfg.ControllerMethod.QQ)
-	mgr.Register(qqCtrl)
-	go func() {
-		defer func() {
-			if r := recover(); r != nil {
-				postLog.Error(fmt.Sprintf("QQ controller panic: %v", r))
-			}
-		}()
-		if err := qqCtrl.Start(); err != nil {
-			postLog.Error("Failed to start QQ controller: " + err.Error())
-		}
-	}()
-
-	// Telegram controller.
-	tgCtrl := telegram.NewTelegramController(cfg.ControllerMethod.Telegram)
-	mgr.Register(tgCtrl)
-	go func() {
-		defer func() {
-			if r := recover(); r != nil {
-				postLog.Error(fmt.Sprintf("Telegram controller panic: %v", r))
-			}
-		}()
-		if err := tgCtrl.Start(); err != nil {
-			postLog.Error("Failed to start Telegram controller: " + err.Error())
-		}
-	}()
-
-	// Email controller (status-only).
-	emailCtrl := pipes.NewEmailController(cfg.ControllerMethod.Email)
-	mgr.Register(emailCtrl)
-	go func() {
-		defer func() {
-			if r := recover(); r != nil {
-				postLog.Error(fmt.Sprintf("Email controller panic: %v", r))
-			}
-		}()
-		if err := emailCtrl.Start(); err != nil {
-			postLog.Error("Failed to start Email controller: " + err.Error())
-		}
-	}()
-
-	// Ntfy controller (status-only).
-	ntfyCtrl := pipes.NewNtfyController(cfg.ControllerMethod.Ntfy)
-	mgr.Register(ntfyCtrl)
-	go func() {
-		defer func() {
-			if r := recover(); r != nil {
-				postLog.Error(fmt.Sprintf("Ntfy controller panic: %v", r))
-			}
-		}()
-		if err := ntfyCtrl.Start(); err != nil {
-			postLog.Error("Failed to start Ntfy controller: " + err.Error())
-		}
-	}()
-
-	// Webhook controller (status-only).
-	webhookCtrl := pipes.NewWebhookController(cfg.ControllerMethod.Webhook)
-	mgr.Register(webhookCtrl)
-	go func() {
-		defer func() {
-			if r := recover(); r != nil {
-				postLog.Error(fmt.Sprintf("Webhook controller panic: %v", r))
-			}
-		}()
-		if err := webhookCtrl.Start(); err != nil {
-			postLog.Error("Failed to start Webhook controller: " + err.Error())
-		}
-	}()
+	mgr.ReplaceAll(buildControllers(cfg), cfg.ControllerMethod)
 }
 
 // startBackgroundTasks starts periodic background goroutines.