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/merge_form.go

@@ -0,0 +1,39 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terminal
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"charm.land/huh/v2"
+)
+
+// MergePullChoice is one selectable open pull request for interactive merge.
+type MergePullChoice struct {
+	Number      int64
+	Title, Head string
+}
+
+// MergeForm collects which pull request to merge.
+type MergeForm interface {
+	SelectPull(context.Context, []MergePullChoice) (int64, error)
+}
+
+// SelectPull prompts for a pull request on stderr.
+func (p *FormPrompter) SelectPull(ctx context.Context, choices []MergePullChoice) (int64, error) {
+	if len(choices) == 0 {
+		return 0, errors.New("no open pull requests match the current branch")
+	}
+	options := make([]huh.Option[int64], 0, len(choices))
+	for _, choice := range choices {
+		options = append(options, huh.NewOption(fmt.Sprintf("#%d: %s (%s)", choice.Number, choice.Title, choice.Head), choice.Number))
+	}
+	selected := choices[0].Number
+	err := p.runForm(ctx, huh.NewForm(huh.NewGroup(
+		huh.NewSelect[int64]().Title("Select a PR to merge:").Options(options...).Value(&selected),
+	)))
+	return selected, err
+}