feat(api): add token introspection and self-deletion endpoint (#37995)

Adds a /api/v1/token endpoint that allows tokens to introspect and
delete themselves.
partially fixes: https://github.com/go-gitea/gitea/issues/33583

Assisted-by: Mistral Vibe:mistral-medium-3.5

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/token.go

@@ -0,0 +1,31 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package structs
+
+import "time"
+
+// CurrentAccessToken represents the metadata of the currently authenticated token.
+// swagger:model CurrentAccessToken
+type CurrentAccessToken struct {
+	// The unique identifier of the access token
+	ID int64 `json:"id"`
+	// The name of the access token
+	Name string `json:"name"`
+	// The scopes granted to this access token
+	Scopes []string `json:"scopes"`
+	// The timestamp when the token was created
+	CreatedAt time.Time `json:"created_at"`
+	// The timestamp when the token was last used
+	LastUsedAt time.Time `json:"last_used_at"`
+	// The owner of the access token
+	User *UserMeta `json:"user"`
+}
+
+// UserMeta represents minimal user information for the token owner.
+type UserMeta struct {
+	// The unique identifier of the user
+	ID int64 `json:"id"`
+	// The username of the user
+	Login string `json:"login"`
+}