Improve "generate new access token" form (#33730)

Fix: https://github.com/go-gitea/gitea/issues/33519

As discussed in [PR
#33614](https://github.com/go-gitea/gitea/pull/33614), the
ScopedAccessTokenSelector Vue component is not particularly useful.

This PR removes the component and reverts to using HTML templates. It
also introduces some (hopefully) useful refactoring.

The Vue component was causing the UX bug reported in the linked issue.
Required form fields are now properly working, as expected (see
screenshot).

![Screenshot from 2025-02-25
22-00-28](https://github.com/user-attachments/assets/41167854-0718-48b0-a3ee-75ca3a7b8b20)

---------

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

models/auth/access_token_scope.go

@@ -5,6 +5,7 @@ package auth
 
 import (
 	"fmt"
+	"slices"
 	"strings"
 
 	"code.gitea.io/gitea/models/perm"
@@ -14,7 +15,7 @@ import (
 type AccessTokenScopeCategory int
 
 const (
-	AccessTokenScopeCategoryActivityPub = iota
+	AccessTokenScopeCategoryActivityPub AccessTokenScopeCategory = iota
 	AccessTokenScopeCategoryAdmin
 	AccessTokenScopeCategoryMisc // WARN: this is now just a placeholder, don't remove it which will change the following values
 	AccessTokenScopeCategoryNotification
@@ -193,6 +194,14 @@ var accessTokenScopes = map[AccessTokenScopeLevel]map[AccessTokenScopeCategory]A
 	},
 }
 
+func GetAccessTokenCategories() (res []string) {
+	for _, cat := range accessTokenScopes[Read] {
+		res = append(res, strings.TrimPrefix(string(cat), "read:"))
+	}
+	slices.Sort(res)
+	return res
+}
+
 // GetRequiredScopes gets the specific scopes for a given level and categories
 func GetRequiredScopes(level AccessTokenScopeLevel, scopeCategories ...AccessTokenScopeCategory) []AccessTokenScope {
 	scopes := make([]AccessTokenScope, 0, len(scopeCategories))
@@ -270,6 +279,9 @@ func (s AccessTokenScope) parse() (accessTokenScopeBitmap, error) {
 
 // StringSlice returns the AccessTokenScope as a []string
 func (s AccessTokenScope) StringSlice() []string {
+	if s == "" {
+		return nil
+	}
 	return strings.Split(string(s), ",")
 }