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/milestone_form.go

@@ -0,0 +1,37 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terminal
+
+import (
+	"context"
+	"strings"
+	"time"
+
+	"charm.land/huh/v2"
+)
+
+// MilestoneFormValues holds interactively collected milestone create fields.
+type MilestoneFormValues struct {
+	Title, Description string
+	Deadline           *time.Time
+}
+
+// MilestoneForm collects interactive milestone create input.
+type MilestoneForm interface {
+	CreateMilestone(context.Context) (MilestoneFormValues, error)
+}
+
+// CreateMilestone runs the interactive milestone create form on stderr.
+func (p *FormPrompter) CreateMilestone(ctx context.Context) (MilestoneFormValues, error) {
+	title, description, deadline := "", "", ""
+	if err := p.runForm(ctx, huh.NewForm(huh.NewGroup(
+		huh.NewInput().Title("Milestone title (required):").Value(&title).Validate(huh.ValidateNotEmpty()),
+		huh.NewText().Title("Milestone description (markdown):").Value(&description),
+		dueDateInput("Milestone deadline:", &deadline),
+	))); err != nil {
+		return MilestoneFormValues{}, err
+	}
+	parsed, err := parseDueDate(deadline)
+	return MilestoneFormValues{Title: strings.TrimSpace(title), Description: description, Deadline: parsed}, err
+}