Fix returning caller eligibility — 1+ calls, not 2+

The 2+ requirement created a catch-22: regulars couldn't return because they
needed 2 calls, but couldn't get a second call without returning. Dynamic
count already prevents flooding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/services/regulars.py

@@ -44,7 +44,7 @@ class RegularCallerService:
         import random
         if not self._regulars:
             return []
-        available = [r for r in self._regulars if len(r.get("call_history", [])) > 1]
+        available = [r for r in self._regulars if len(r.get("call_history", [])) > 0]
         if not available:
             return []
         return random.sample(available, min(count, len(available)))