fix: Various security fixes (#38103) (#38151)

Backport #38103

- Enforce org visibility on organization label read endpoints (private
org labels no longer leak to non-members).
- Block fork sync (`merge-upstream`) when the base repo is no longer
readable (stops pulling commits after a parent goes private).
- Remove `REVERSE_PROXY_LIMIT` / `REVERSE_PROXY_TRUSTED_PROXIES` from
the Docker `app.ini` templates (the `= *` default allowed
`X-WEBAUTH-USER` impersonation; reverse-proxy auth is now opt-in and
admin-configured).
- Enforce single-use TOTP passcodes across web login, password-reset,
and Basic-Auth `X-Gitea-OTP` (fixes a TOCTOU race and a stateless
replay).
- Re-check branch write permission for every ref in a push (the
pre-receive hook cached the first ref's result, letting a per-branch
maintainer-edit grant escalate to full repo write).

---------

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

models/auth/twofactor_test.go

@@ -0,0 +1,47 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package auth_test
+
+import (
+	"testing"
+	"time"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/unittest"
+
+	"github.com/pquerna/otp/totp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTwoFactorValidateAndConsumeTOTP(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	key, err := totp.Generate(totp.GenerateOpts{SecretSize: 40, Issuer: "gitea-test", AccountName: "consume"})
+	require.NoError(t, err)
+
+	tfa := &auth_model.TwoFactor{UID: 1}
+	require.NoError(t, tfa.SetSecret(key.Secret()))
+	require.NoError(t, auth_model.NewTwoFactor(t.Context(), tfa))
+
+	passcode, err := totp.GenerateCode(key.Secret(), time.Now())
+	require.NoError(t, err)
+
+	// first use of a valid passcode succeeds
+	ok, err := tfa.ValidateAndConsumeTOTP(t.Context(), passcode)
+	require.NoError(t, err)
+	assert.True(t, ok)
+
+	// replaying the same passcode is refused, even when still inside the TOTP validity window
+	reloaded, err := auth_model.GetTwoFactorByUID(t.Context(), tfa.UID)
+	require.NoError(t, err)
+	ok, err = reloaded.ValidateAndConsumeTOTP(t.Context(), passcode)
+	require.NoError(t, err)
+	assert.False(t, ok)
+
+	// an invalid passcode is rejected without consuming anything
+	ok, err = reloaded.ValidateAndConsumeTOTP(t.Context(), "000000")
+	require.NoError(t, err)
+	assert.False(t, ok)
+}