feat(reddit): honest tiering — OpenCLI / rdt-cli, no zero-config path

- live-verified 2026-06: anonymous .json endpoints are 403-blocked (all
  variants) and the official API closed self-service registration in
  2025-11 — so the channel now says plainly: every Reddit backend needs
  a logged-in session, mainland China needs a proxy
- backends = [OpenCLI, rdt-cli]: OpenCLI rides the browser session
  (desktop preferred); rdt-cli stays for servers and existing installs
  (upstream unmaintained since 2026-03, noted in the ok message)
- install: desktop routes to OpenCLI, server installs rdt-cli from the
  pinned git source (split out as _install_rdt_cli)
- skill/references/social.md: Reddit section rewritten as two backend
  command groups + a PRAW note scoped to users who already hold
  pre-2025-11 credentials (explicitly not recommended for new users)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_cli.py

@@ -60,7 +60,7 @@ class TestCLI:
         assert auth_token == "token123"
         assert ct0 == "ct0abc"
 
-    def test_install_reddit_deps_prefers_github_source(self, monkeypatch, capsys):
+    def test_install_rdt_cli_prefers_github_source(self, monkeypatch, capsys):
         state = {"rdt_installed": False}
         commands = []
 
@@ -79,12 +79,28 @@ class TestCLI:
         monkeypatch.setattr(shutil, "which", fake_which)
         monkeypatch.setattr(subprocess, "run", fake_run)
 
-        cli._install_reddit_deps()
+        cli._install_rdt_cli()
 
         out = capsys.readouterr().out
         assert commands == [["pipx", "install", cli._RDT_GIT_SOURCE]]
         assert "✅ rdt-cli installed" in out
 
+    def test_install_reddit_deps_routes_by_environment(self, monkeypatch):
+        """桌面 → OpenCLI;服务器 → rdt-cli(钉 git 源)。"""
+        calls = []
+        monkeypatch.setattr(cli, "_install_opencli_deps", lambda: calls.append("opencli"))
+        monkeypatch.setattr(cli, "_install_rdt_cli", lambda: calls.append("rdt"))
+        monkeypatch.setattr(shutil, "which", lambda _: None)
+
+        monkeypatch.setattr(cli, "_detect_environment", lambda: "local")
+        cli._install_reddit_deps()
+        assert calls == ["opencli"]
+
+        calls.clear()
+        monkeypatch.setattr(cli, "_detect_environment", lambda: "server")
+        cli._install_reddit_deps()
+        assert calls == ["rdt"]
+
 
 class TestCheckUpdateRetry:
     def test_retry_timeout_classification(self):