Fix snake_case detection to accept single-word lowercase identifiers

DetectCasing's snake_case regex required at least one underscore, so
single-word lowercase names like `currency` fell into a separate
"lowercase" bucket. When a tool had params like
`origin_country, hs_code, currency`, the deterministic
pn_consistent_casing check produced the false positive
"Parameter 'currency' uses lowercase but other params use snake_case."

Use `*` (zero-or-more underscores) so single-word lowercase names
classify as snake_case. The "lowercase" branch becomes unreachable
and is removed. The tool-name casing regex at line 172 already used
this form; this brings DetectCasing into agreement.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ashragrawal

src/Microsoft.Agents.A365.DevTools.Cli/Services/Evaluate/ChecklistGenerator.cs

@@ -1048,7 +1048,9 @@ private static string DetectCasing(string name)
             return "empty";
         }
 
-        if (Regex.IsMatch(name, @"^[a-z][a-z0-9]*(_[a-z0-9]+)+$"))
+        // Single-word lowercase identifiers (e.g. "currency") are valid snake_case
+        // by formal definition; `*` (zero-or-more underscores) is correct, not `+`.
+        if (Regex.IsMatch(name, @"^[a-z][a-z0-9]*(_[a-z0-9]+)*$"))
         {
             return "snake_case";
         }
@@ -1068,11 +1070,6 @@ private static string DetectCasing(string name)
             return "PascalCase";
         }
 
-        if (Regex.IsMatch(name, @"^[a-z][a-z0-9]*$"))
-        {
-            return "lowercase";
-        }
-
         return "mixed";
     }