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>

agent_reach/cli.py

@@ -774,7 +774,24 @@ def _install_opencli_deps():
 
 
 def _install_reddit_deps():
-    """Install rdt-cli for Reddit search + reading."""
+    """Set up Reddit — desktop prefers OpenCLI, rdt-cli for servers/legacy.
+
+    No zero-config path exists (anonymous .json blocked, official API
+    approval-gated since 2025-11) — every backend needs a logged-in session.
+    """
+    if _detect_environment() != "server":
+        _install_opencli_deps()
+        print("  Reddit 走 OpenCLI（浏览器里登录过 reddit.com 即可用）")
+        import shutil
+        if shutil.which("rdt"):
+            print("  ✅ 检测到存量 rdt-cli，将作为备选后端继续可用")
+        return
+
+    _install_rdt_cli()
+
+
+def _install_rdt_cli():
+    """Install rdt-cli (pinned git source — PyPI lags upstream)."""
     import shutil
     import subprocess