revert: tea 1.0 rewrite (#1122–#1126) (#1146)

Reverts #1126, #1125, #1124, #1123 and #1122.

`go.mod` keeps the Go 1.26 line with toolchain `go1.26.9` (instead of the original `go1.26.6`) so the security fix from #1131 isn't lost.

reopens #69
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Reviewed-on: https://gitea.com/gitea/tea/pulls/1146
Reviewed-by: TheFox0x7 <95654+thefox0x7@noreply.gitea.com>

modules/httputil/httputil.go

@@ -0,0 +1,46 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package httputil
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/http"
+	"runtime"
+
+	"gitea.dev/tea/modules/version"
+)
+
+// UserAgent returns the standard User-Agent string for tea.
+func UserAgent() string {
+	ua := fmt.Sprintf("tea/%s (%s/%s)", version.Version, runtime.GOOS, runtime.GOARCH)
+	if version.SDK != "" {
+		ua += fmt.Sprintf(" go-sdk/%s", version.SDK)
+	}
+	return ua
+}
+
+// WrapTransport returns tea's standard HTTP transport: an *http.Transport
+// preset with tea's connection / response-header timeouts (see timeoutTransport)
+// and decorated to add the User-Agent header on every request. The supplied
+// tlsConfig is attached as-is (nil is fine); callers use it for insecure /
+// skip-verify logins. This is the single entry point for building a tea HTTP
+// client transport, so the timeouts can't be accidentally omitted.
+func WrapTransport(tlsConfig *tls.Config) http.RoundTripper {
+	return &userAgentTransport{base: timeoutTransport(tlsConfig)}
+}
+
+type userAgentTransport struct {
+	base http.RoundTripper
+}
+
+func (t *userAgentTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	// Set the UA at the transport so every client built from WrapTransport
+	// identifies itself, including the non-SDK clients (oauth2 flow, token
+	// refresh) that never pass through the SDK's own SetUserAgent. For SDK
+	// clients this overlaps gitea.SetUserAgent; both use httputil.UserAgent(),
+	// so the duplicate Header.Set is a no-op.
+	req.Header.Set("User-Agent", UserAgent())
+	return t.base.RoundTrip(req)
+}