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>

build/openapi3gen/enumscan_test.go

@@ -6,10 +6,19 @@ package openapi3gen
 import (
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"testing"
 )
 
+func single(got map[string][]string, key string) string {
+	v := got[key]
+	if len(v) != 1 {
+		return ""
+	}
+	return v[0]
+}
+
 func TestEnumKey_sortsAndJoins(t *testing.T) {
 	key := EnumKey([]any{"b", "a", "c"})
 	if key != "a|b|c" {
@@ -47,7 +56,7 @@ const (
 		t.Fatalf("ScanSwaggerEnumTypes: %v", err)
 	}
 	wantKey := EnumKey([]any{"red", "green", "blue"})
-	if got[wantKey] != "Color" {
+	if single(got, wantKey) != "Color" {
 		t.Fatalf("map[%q] = %q, want %q", wantKey, got[wantKey], "Color")
 	}
 }
@@ -98,13 +107,14 @@ const (
 		t.Fatal(err)
 	}
 
-	_, err := ScanSwaggerEnumTypes([]string{dir})
-	if err == nil {
-		t.Fatal("expected collision error, got nil")
+	got, err := ScanSwaggerEnumTypes([]string{dir})
+	if err != nil {
+		t.Fatalf("ScanSwaggerEnumTypes: %v", err)
 	}
-	msg := err.Error()
-	if !strings.Contains(msg, "Alpha") || !strings.Contains(msg, "Beta") {
-		t.Fatalf("error %q should mention both Alpha and Beta", msg)
+	key := EnumKey([]any{"x", "y"})
+	names := got[key]
+	if !slices.Equal(names, []string{"Alpha", "Beta"}) {
+		t.Fatalf("map[%q] = %v, want [Alpha Beta]", key, names)
 	}
 }
 
@@ -168,7 +178,7 @@ type Hue string
 		t.Fatalf("ScanSwaggerEnumTypes: %v", err)
 	}
 	wantKey := EnumKey([]any{"a", "b"})
-	if got[wantKey] != "Hue" {
+	if single(got, wantKey) != "Hue" {
 		t.Fatalf("map[%q] = %q, want %q", wantKey, got[wantKey], "Hue")
 	}
 }
@@ -194,7 +204,7 @@ type Shade string
 		t.Fatalf("ScanSwaggerEnumTypes: %v", err)
 	}
 	wantKey := EnumKey([]any{"dark", "light"})
-	if got[wantKey] != "Shade" {
+	if single(got, wantKey) != "Shade" {
 		t.Fatalf("map[%q] = %q, want %q", wantKey, got[wantKey], "Shade")
 	}
 }
@@ -230,10 +240,10 @@ const (
 	}
 	colorKey := EnumKey([]any{"red", "blue"})
 	shadeKey := EnumKey([]any{"dark", "light"})
-	if got[colorKey] != "Color" {
+	if single(got, colorKey) != "Color" {
 		t.Fatalf("Color: map[%q] = %q, want %q", colorKey, got[colorKey], "Color")
 	}
-	if got[shadeKey] != "Shade" {
+	if single(got, shadeKey) != "Shade" {
 		t.Fatalf("Shade: map[%q] = %q, want %q", shadeKey, got[shadeKey], "Shade")
 	}
 }