Fix malformed bullet point characters in error messages and logs

[Copilot]

Replaced malformed bullet characters (�) with proper Unicode bullet points (•) across error logging and exception formatting.

Changes

• ConfigService.cs: Fixed validation error and warning log messages (2 instances)
• Agent365Exception.cs: Fixed error details, context formatting, and helper methods (3 instances)
• ConfigurationValidationException.cs: Fixed Azure naming rules contextual help (1 instance)

Example

// Before
_logger?.LogError("  � {Error}", error);

// After  
_logger?.LogError("  • {Error}", error);

Total: 6 instances corrected across 3 files.

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