refactor: add terminal output and forms package (#1124)

- `internal/terminal`: streams and the prompting policy, interactive forms (issue, PR, review, merge, milestone), editor / pager / browser launching, JSON and `--jq` output.
- An aligned table renderer and a record renderer for human output; both strip control and escape characters from server-supplied text so titles and bodies cannot inject terminal sequences.

Reviewed-on: https://gitea.com/gitea/tea/pulls/1124
Reviewed-by: TheFox0x7 <95654+thefox0x7@noreply.gitea.com>

internal/terminal/browser.go

@@ -0,0 +1,59 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terminal
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/url"
+	"os/exec"
+	"runtime"
+	"strings"
+)
+
+// Browser opens an explicitly requested resource using a configured command.
+type Browser interface {
+	Open(context.Context, string, string) error
+}
+
+// SystemBrowser runs the browser without a shell and routes diagnostics to stderr.
+type SystemBrowser struct{ ErrOut io.Writer }
+
+// Open validates the resource and invokes the selected browser directly.
+func (b SystemBrowser) Open(ctx context.Context, resource, command string) error {
+	u, err := url.Parse(resource)
+	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" || u.User != nil || strings.ContainsAny(resource, "\x00\r\n") {
+		return errors.New("browser requires an HTTP or HTTPS resource URL without credentials")
+	}
+	var args []string
+	if command == "" || command == "auto" {
+		switch runtime.GOOS {
+		case "darwin":
+			args = []string{"open"}
+		case "windows":
+			args = []string{"rundll32", "url.dll,FileProtocolHandler"}
+		default:
+			args = []string{"xdg-open"}
+		}
+	} else {
+		if command == "never" {
+			return errors.New("browser opening is disabled; configure browser or BROWSER")
+		}
+		var ok bool
+		if args, ok = commandArgs(command); !ok {
+			return errors.New("browser command contains malformed quoted arguments")
+		}
+	}
+	process := exec.CommandContext(ctx, args[0], append(args[1:], resource)...)
+	process.Stdout, process.Stderr = b.ErrOut, b.ErrOut
+	if err := process.Run(); err != nil {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		return fmt.Errorf("browser could not be opened; configure browser or BROWSER: %w", err)
+	}
+	return nil
+}