fix(security): TICKET-009 add HTTP timeouts to notifier clients

- Added TestSlack_ClientHasTimeout to verify 10-second timeout
- Added TestTeams_ClientHasTimeout to verify 10-second timeout
- Added TestPagerDuty_ClientHasTimeout to verify 10-second timeout
- Added TestOpsGenie_ClientHasTimeout to verify 10-second timeout
- All notifiers already configured with 10 second timeout in New()
- Tests verify timeout is set and matches expected value

internal/config/config.go

@@ -147,7 +147,11 @@ type RateLimitConfig struct {
 
 // CORSConfig contains CORS configuration.
 type CORSConfig struct {
-	AllowedOrigins []string // Allowed origins; empty = same-origin only; ["*"] = all
+	// AllowedOrigins is a list of allowed origins for CORS requests.
+	// Security default: empty list denies all CORS requests (same-origin only).
+	// ["*"] allows all origins (development/demo mode only, security risk).
+	// Specific origins (e.g., ["https://app.example.com"]) whitelist only those origins.
+	AllowedOrigins []string
 }
 
 // Load reads configuration from environment variables and returns a Config.