fix(config): improve validation error messages for edge_connect config

Clarified error messages to help diagnose configuration issues:
- Changed "edge_connect_url" to "edge_connect.url" to match actual TOML structure
- Added helpful note about common mistake of using hyphens instead of underscores in TOML section names

This addresses confusion when users accidentally use [edge-connect] instead of [edge_connect].

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

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

config/config.go

@@ -28,7 +28,7 @@ func NewConfig(cfgFile string) (*Config, error) {
 	}
 
 	if err := config.Validate(); err != nil {
-		return nil, fmt.Errorf("error validating config: %w", err)
+		return nil, fmt.Errorf("error validating config: %w (note: TOML section must be [edge_connect] not [edge-connect])", err)
 	}
 	return &config, nil
 }
@@ -72,7 +72,7 @@ func (c *Config) Validate() error {
 	}
 
 	if c.EdgeConnect.URL == "" {
-		return fmt.Errorf("edge_connect_url is not defined in provider config")
+		return fmt.Errorf("edge_connect.url is not defined in provider config")
 	}
 
 	return nil