Add terraform state registry (#36710)

Adds terraform/opentofu state registry with locking. Implements: https://github.com/go-gitea/gitea/issues/33644. I also checked [encrypted state](https://opentofu.org/docs/language/state/encryption), it works out of the box.

Docs PR: https://gitea.com/gitea/docs/pulls/357

---------

Co-authored-by: Andras Elso <elso.andras@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/packages/terraform/terraform_test.go

@@ -0,0 +1,36 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terraform
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestValidatePackageName(t *testing.T) {
+	bad := []string{
+		"",
+		".",
+		"..",
+		"-",
+		"a?b",
+		"a b",
+		"a/b",
+	}
+	for _, name := range bad {
+		assert.False(t, isValidPackageName(name), "bad=%q", name)
+	}
+
+	good := []string{
+		"a",
+		"1",
+		"a-",
+		"a_b",
+		"c.d+",
+	}
+	for _, name := range good {
+		assert.True(t, isValidPackageName(name), "good=%q", name)
+	}
+}