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.go

@@ -14,6 +14,7 @@ import (
 	"gitea.dev/models/unit"
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/log"
+	"gitea.dev/modules/structs"
 	"gitea.dev/modules/util"
 
 	"xorm.io/builder"
@@ -81,9 +82,36 @@ type Team struct {
 	Members                 []*user_model.User `xorm:"-"`
 	NumRepos                int
 	NumMembers              int
-	Units                   []*TeamUnit `xorm:"-"`
-	IncludesAllRepositories bool        `xorm:"NOT NULL DEFAULT false"`
-	CanCreateOrgRepo        bool        `xorm:"NOT NULL DEFAULT false"`
+	Units                   []*TeamUnit         `xorm:"-"`
+	IncludesAllRepositories bool                `xorm:"NOT NULL DEFAULT false"`
+	CanCreateOrgRepo        bool                `xorm:"NOT NULL DEFAULT false"`
+	Visibility              structs.VisibleType `xorm:"NOT NULL DEFAULT 2"`
+}
+
+func (t *Team) IsPublic() bool  { return t.Visibility.IsPublic() }
+func (t *Team) IsLimited() bool { return t.Visibility.IsLimited() }
+func (t *Team) IsPrivate() bool { return t.Visibility.IsPrivate() }
+
+// CanNonMemberReadMeta reports whether a non-member, non-owner doer may read
+// the team's metadata, based on the team's visibility tier and the parent org's
+// visibility. Privileged callers (site admins, org owners, team members) are
+// decided by the caller before reaching here.
+func (t *Team) CanNonMemberReadMeta(ctx context.Context, org, doer *user_model.User) (bool, error) {
+	switch t.Visibility {
+	case structs.VisibleTypePublic:
+		return HasOrgOrUserVisible(ctx, org, doer), nil
+	case structs.VisibleTypeLimited:
+		return IsOrganizationMember(ctx, t.OrgID, doer.ID)
+	default:
+		return false, nil
+	}
+}
+
+func NormalizeTeamVisibility(s string) structs.VisibleType {
+	if vt, ok := structs.VisibilityModes[s]; ok {
+		return vt
+	}
+	return structs.VisibleTypePrivate
 }
 
 func init() {