Fix decimal precision for CategoryMapping.Confidence field

Add explicit column type configuration for Confidence field to avoid
SQL Server truncation warnings. Use decimal(5,4) to store values from
0.0000 to 1.0000 with 4 decimal places of precision.

Also add MaxLength constraint for CreatedBy field.

Migration applied successfully to database.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.claude/settings.local.json

@@ -4,7 +4,10 @@
       "Bash(git add:*)",
       "Bash(git commit:*)",
       "Bash(dotnet ef migrations add:*)",
-      "Bash(dotnet build)"
+      "Bash(dotnet build)",
+      "Bash(dotnet ef database:*)",
+      "Bash(dotnet ef migrations:*)",
+      "Bash(git reset:*)"
     ],
     "deny": [],
     "ask": []