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>

internal/command/complete.go

@@ -0,0 +1,67 @@
+package command
+
+import "strings"
+
+func completeFirstToken(line, token string, cands []string) (string, []string) {
+	matches := filterPrefix(cands, token)
+	if len(matches) == 0 {
+		return line, nil
+	}
+	if len(matches) == 1 {
+		prefix := strings.TrimSuffix(line, token)
+		return prefix + matches[0] + " ", matches
+	}
+	return line, matches
+}
+
+func filterPrefix(cands []string, cur string) []string {
+	if cur == "" {
+		return append([]string{}, cands...)
+	}
+	res := make([]string, 0, len(cands))
+	for _, c := range cands {
+		if strings.HasPrefix(strings.ToLower(c), strings.ToLower(cur)) {
+			res = append(res, c)
+		}
+	}
+	return res
+}
+
+func completeForward(args []string) []string {
+	if len(args) <= 2 {
+		return []string{"list", "add", "remove", "enable", "disable", "update", "stats"}
+	}
+
+	if len(args) == 3 && args[1] == "add" {
+		return []string{"tcp", "udp"}
+	}
+
+	if len(args) == 4 && args[1] == "update" {
+		return []string{"tcp", "udp"}
+	}
+
+	return nil
+}
+
+func completePlugin(args []string) []string {
+	if len(args) <= 2 {
+		return []string{"list", "load", "unload", "enable", "disable", "reload"}
+	}
+	return nil
+}
+
+func completeMode(args []string) []string {
+	if len(args) <= 2 {
+		return []string{"show", "set"}
+	}
+
+	if len(args) == 3 && args[1] == "set" {
+		return []string{"in", "out", "end", "frame", "timestamp", "timefmt"}
+	}
+
+	if len(args) == 4 && args[1] == "set" && args[2] == "timestamp" {
+		return []string{"on", "off"}
+	}
+
+	return nil
+}