fix(review): four findings from adversarial Codex review round 1

- twitter: align backend selection with the two-phase findings pattern —
  an unauthenticated twitter-cli (warn) no longer blocks a fully-working
  OpenCLI (ok) further down the candidate list
- watch: use _is_newer_version like check-update (the != comparison kept
  the downgrade prompt this branch fixed elsewhere)
- uninstall: third copy of the skill-dir removal also gets the symlink
  guard (full `agent-reach uninstall` path)
- doctor: a stale active_backend from a previous check on the singleton
  channel no longer leaks into an errored result

+4 regression tests (162 total).

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

agent_reach/cli.py

@@ -1387,7 +1387,10 @@ def _cmd_uninstall(args):
                 print(f"[dry-run] Would remove {platform_name} skill: {skill_path}")
             else:
                 try:
-                    shutil.rmtree(skill_path)
+                    if os.path.islink(skill_path):
+                        os.unlink(skill_path)
+                    else:
+                        shutil.rmtree(skill_path)
                     print(f"  Removed {platform_name} skill: {skill_path}")
                     removed_any = True
                 except Exception as e:
@@ -1762,7 +1765,7 @@ def _cmd_watch():
     if not err and resp and resp.status_code == 200:
         data = resp.json()
         latest = data.get("tag_name", "").lstrip("v")
-        if latest and latest != __version__:
+        if latest and _is_newer_version(latest, __version__):
             update_available = True
             new_version = latest
             release_body = data.get("body", "")