fix: various security fixes (#38406)

Addresses a batch of privately reported security issues, grouped by
area:

- **SSRF** - migration PR-patch/asset fetches, OAuth2 avatar & OpenID
discovery, pull-mirror URL re-validation, and the outbound proxy path.
- **Access-token scope** - prevent scope escalation on token creation;
keep public-only tokens confined (feeds, packages, Actions listings,
star/watch lists, limited/private owners).
- **Access control / disclosure** - go-get default-branch leak, webhook
authorization-header leak, watch clearing on private transitions,
label/attachment scoping.
- **Denial of service** - input bounds for npm dist-tags, Debian control
files, Arch file lists, and SSH keys.

### 📌 Attention for site admins

Not breaking - existing configs keep working - but two changes are worth
a look:

- **New SSRF protection** Outbound requests (migrations, OAuth2 avatars,
OpenID discovery, pull mirrors, proxy path) are now validated against
the allow/block host lists. If your instance legitimately reaches
internal hosts, you may need to add them to
`[security].ALLOWED_HOST_LIST` (and the relevant `ALLOW_LOCALNETWORKS`
settings).
- **Deprecation** `[webhook].ALLOWED_HOST_LIST` is deprecated and will
be removed in a future release. Use `[security].ALLOWED_HOST_LIST`
instead; the old key still works for now.

---------

Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

tests/integration/api_user_email_test.go

@@ -8,12 +8,34 @@ import (
 	"testing"
 
 	auth_model "gitea.dev/models/auth"
+	"gitea.dev/modules/setting"
 	api "gitea.dev/modules/structs"
 	"gitea.dev/tests"
 
 	"github.com/stretchr/testify/assert"
 )
 
+// TestAPIManageEmailsFeatureDisabled ensures the email management API honors the
+// manage_credentials feature restriction, matching the web UI.
+func TestAPIManageEmailsFeatureDisabled(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	session := loginUser(t, "user2")
+	token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteUser)
+
+	WithDisabledFeatures(t, setting.UserFeatureManageCredentials)
+
+	addReq := NewRequestWithJSON(t, "POST", "/api/v1/user/emails", &api.CreateEmailOption{
+		Emails: []string{"user2-3@example.com"},
+	}).AddTokenAuth(token)
+	MakeRequest(t, addReq, http.StatusNotFound)
+
+	delReq := NewRequestWithJSON(t, "DELETE", "/api/v1/user/emails", &api.DeleteEmailOption{
+		Emails: []string{"user2-2@example.com"},
+	}).AddTokenAuth(token)
+	MakeRequest(t, delReq, http.StatusNotFound)
+}
+
 func TestAPIListEmails(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()