feat(org): add team visibility so org members can discover teams (#37680)

Closes #37670.

Today, org members in Gitea only see teams they're a member of. In
larger orgs that hurts onboarding and discoverability — there's no way
to look up which team owns what without asking around. GitHub solves
this with a per-team visibility setting; this PR brings the same model
to Gitea.

## What changes

- Every team gets a `visibility` setting:
- `private` *(default)* — only team members and org owners can see the
team. Same as today's behavior.
- `limited` — listable by any member of the organization. Members and
the repos the team has access to are visible too. Non-org-members still
see nothing.
  - `public` — listable by any signed-in user.
- The Owners team visibility is fixed and cannot be changed via
settings.
- Existing teams default to `private`, so this is a no-op for anyone who
doesn't change anything.

## API

- `Team`, `CreateTeamOption`, `EditTeamOption` all gain a `visibility`
field (string enum: `private` | `limited` | `public`).
- `GET /orgs/{org}/teams` and `/orgs/{org}/teams/search` now apply the
same visibility rules as the web UI:
  - site admins and org owners still see every team
- other org members see their own teams plus any `limited` or `public`
team
  - `private` teams are no longer leaked through these endpoints
- Swagger/OpenAPI specs regenerated.

## UI

View from admin2 (not an owner):
<img width="1669" height="726"
src="https://github.com/user-attachments/assets/daf4bccb-644b-4426-b178-71963aeaf73b"
/>

View from admin (owner):

<img width="2559" height="863"
src="https://github.com/user-attachments/assets/4f22cebc-e9df-4fd2-8ed4-724d31fadb7a"
/>

---------

Signed-off-by: bircni <bircni@icloud.com>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/organization/team_list.go

@@ -10,6 +10,8 @@ import (
 	"gitea.dev/models/db"
 	"gitea.dev/models/perm"
 	"gitea.dev/models/unit"
+	user_model "gitea.dev/models/user"
+	"gitea.dev/modules/structs"
 
 	"xorm.io/builder"
 )
@@ -50,9 +52,15 @@ type SearchTeamOptions struct {
 	Keyword     string
 	OrgID       int64
 	IncludeDesc bool
+	// IncludeVisibilities, when combined with UserID, also returns teams whose
+	// visibility is in this list, even if UserID is not a member. Typical values:
+	//   - {limited,public} for org members
+	//   - {public} for signed-in users who are not org members
+	// Leave empty to return only teams the user is a member of.
+	IncludeVisibilities []structs.VisibleType
 }
 
-func (opts *SearchTeamOptions) toCond() builder.Cond {
+func (opts *SearchTeamOptions) applyToSession(sess db.SQLSession) {
 	cond := builder.NewCond()
 
 	if len(opts.Keyword) > 0 {
@@ -68,11 +76,51 @@ func (opts *SearchTeamOptions) toCond() builder.Cond {
 		cond = cond.And(builder.Eq{"`team`.org_id": opts.OrgID})
 	}
 
-	if opts.UserID > 0 {
+	switch {
+	case opts.UserID > 0 && len(opts.IncludeVisibilities) > 0:
+		sess = sess.Join("LEFT", "team_user", "team_user.team_id = team.id AND team_user.uid = ?", opts.UserID)
+		cond = cond.And(builder.Or(
+			builder.Eq{"team_user.uid": opts.UserID},
+			builder.In("`team`.visibility", opts.IncludeVisibilities),
+		))
+	case opts.UserID > 0:
+		sess = sess.Join("INNER", "team_user", "team_user.team_id = team.id")
 		cond = cond.And(builder.Eq{"team_user.uid": opts.UserID})
+	case len(opts.IncludeVisibilities) > 0:
+		cond = cond.And(builder.In("`team`.visibility", opts.IncludeVisibilities))
 	}
+	sess.Where(cond)
+}
 
-	return cond
+func VisibleTeamVisibilitiesFor(isOrgMember, isSignedIn bool) []structs.VisibleType {
+	switch {
+	case isOrgMember:
+		return []structs.VisibleType{structs.VisibleTypeLimited, structs.VisibleTypePublic}
+	case isSignedIn:
+		return []structs.VisibleType{structs.VisibleTypePublic}
+	default:
+		return nil
+	}
+}
+
+func ApplyTeamListFilter(ctx context.Context, orgID int64, viewer *user_model.User, isSignedIn bool, opts *SearchTeamOptions) error {
+	if viewer.IsAdmin {
+		return nil
+	}
+	isOwner, err := IsOrganizationOwner(ctx, orgID, viewer.ID)
+	if err != nil {
+		return err
+	}
+	if isOwner {
+		return nil
+	}
+	isOrgMember, err := IsOrganizationMember(ctx, orgID, viewer.ID)
+	if err != nil {
+		return err
+	}
+	opts.UserID = viewer.ID
+	opts.IncludeVisibilities = VisibleTeamVisibilitiesFor(isOrgMember, isSignedIn)
+	return nil
 }
 
 // SearchTeam search for teams. Caller is responsible to check permissions.
@@ -80,15 +128,12 @@ func SearchTeam(ctx context.Context, opts *SearchTeamOptions) (TeamList, int64,
 	sess := db.GetEngine(ctx)
 
 	opts.SetDefaultValues()
-	cond := opts.toCond()
+	opts.applyToSession(sess)
 
-	if opts.UserID > 0 {
-		sess = sess.Join("INNER", "team_user", "team_user.team_id = team.id")
-	}
 	db.SetSessionPagination(sess, opts)
 
 	teams := make([]*Team, 0, opts.PageSize)
-	count, err := sess.Where(cond).OrderBy("CASE WHEN name=? THEN '' ELSE lower_name END", OwnerTeamName).FindAndCount(&teams)
+	count, err := sess.OrderBy("CASE WHEN name=? THEN '' ELSE lower_name END", OwnerTeamName).FindAndCount(&teams)
 	if err != nil {
 		return nil, 0, err
 	}