Add read-only web UI

Serves Pete's classified-story archive over HTTP alongside the Matrix
bot. Three sections (gaming/tech/politics), Animal-Crossing-vibe Tailwind
templates, day/night palette driven by the visitor's browser clock.
Web port configurable via web.listen_addr and ${PETE_WEB_PORT} in
docker-compose. Tailwind built in a node stage in the Dockerfile so
deployments don't need node at runtime.

main.go

@@ -18,6 +18,7 @@ import (
 	"pete/internal/poster"
 	"pete/internal/scheduler"
 	"pete/internal/storage"
+	"pete/internal/web"
 
 	"maunium.net/go/mautrix/id"
 )
@@ -226,6 +227,16 @@ func main() {
 		}
 	}
 
+	// Start the read-only web UI alongside the Matrix bot.
+	if cfg.Web.Enabled {
+		ws, err := web.New(cfg.Web)
+		if err != nil {
+			slog.Error("web server init failed", "err", err)
+		} else {
+			go ws.Start(ctx)
+		}
+	}
+
 	// Run maintenance on startup
 	storage.RunMaintenance(cfg.Storage.RecentWindowHours, cfg.Storage.ClassificationLogDays)