refactor: split termapp into proper internal packages

Replace monolithic internal/termapp with proper separation:
- internal/app: App struct, lifecycle, output loops
- internal/command: CommandHost interface, Dispatcher, handlers
- internal/tui: Model, hotkeys, panels, render (with panelError + border fixes)
- internal/console: RunConsole, escape parsing, entry point logic
- cmd/serialterminal: thin main() calling console.Run()

Eliminate global vars (cfg, sess, out) via dependency injection.
Break App->CommandDispatcher cycle via CommandHost interface.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

cmd/serialterminal/main.go

@@ -1,7 +1,15 @@
 package main
 
-import "github.com/jixishi/SerialTerminalForWindowsTerminal/internal/termapp"
+import (
+	"log"
+
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/internal/console"
+)
+
+func init() {
+	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile | log.Lmsgprefix)
+}
 
 func main() {
-	termapp.Run()
+	console.Run()
 }